add travis for continuous integration testing

[cesine]

How this was tested

Node <= 0.12 https://travis-ci.com/github/cesine/grunt-eco/jobs/363481531 fails due to mde/ejs#534

/home/travis/build/cesine/grunt-eco/node_modules/grunt-contrib-nodeunit/node_modules/nodeunit-x/node_modules/ejs/postinstall.js:9
let envDisable = isTrue(process.env.DISABLE_OPENCOLLECTIVE) || isTrue(process.
^^^
SyntaxError: Unexpected strict mode reserved word

Node <= 6 https://travis-ci.com/github/cesine/grunt-eco/jobs/363475715 fails due to mkdirp

$ grunt
/home/travis/build/cesine/grunt-eco/node_modules/mkdirp/lib/opts-arg.js:7
    opts = { mode: 0o777, fs, ...opts }
                              ^^^
SyntaxError: Unexpected token ...
    at createScript (vm.js:56:10)
    at Object.runInThisContext (vm.js:97:10)
    at Module._compile (module.js:549:28)
    at Object.Module._extensions..js (module.js:586:10)
    at Module.load (module.js:494:32)
    at tryModuleLoad (module.js:453:12)
    at Function.Module._load (module.js:445:3)
    at Module.require (module.js:504:17)
    at require (internal/module.js:20:19)
    at Object.<anonymous> (/home/travis/build/cesine/grunt-eco/node_modules/mkdirp/index.js:1:79)
The command "grunt" exited with 1.
cache.2
store build cache
0.00s1.62snothing changed
Done. Your build exited with 1.

$ npm ls mkdirp
grunt-eco@0.1.3 /Users/gchiodo/git/grunt-eco
├─┬ grunt@1.2.1
│ └── mkdirp@1.0.4
└─┬ grunt-contrib-nodeunit@2.1.0
  └─┬ nodeunit-x@0.13.0
    └─┬ tap@12.7.0
      ├── mkdirp@0.5.5
      └─┬ nyc@14.1.1
        └─┬ spawn-wrap@1.4.3
          └── mkdirp@0.5.5

The root cause is mkdir is using es6 after v 1.0.0 isaacs/node-mkdirp@ed0ae94#diff-3ca2c4508c333566c2fe17e2a75c5863

and grunt dropped support for older versions of node in gruntjs/grunt@4bfa98e#diff-b9cfc7f2cdf78a7f4b91a753d10865a2 v 1.1.0

• Lock the dev deps of grunt to be able to verify older node versions are working with this lib in CI (keep the peer dep open-ended so that consumers have flexibilty) a52a148

Node > 8 https://travis-ci.com/github/cesine/grunt-eco/jobs/363475717#L216

$ grunt
(node:5175) [DEP0025] DeprecationWarning: sys is deprecated. Use util instead.
Running "jshint:gruntfile" (jshint) task
>> 1 file lint free.
Running "jshint:tasks" (jshint) task
>> 1 file lint free.
Running "jshint:tests" (jshint) task
>> 1 file lint free.
Running "clean:test" (clean) task
>> 0 paths cleaned.
Running "eco:filesTest" (eco) task
File tmp/filesTest/all.js created.
File tmp/filesTest/flatOnly.js created.
Running "eco:srcDestTest" (eco) task
File tmp/srcDestTest/all.js created.
Running "eco:expandTest" (eco) task
File tmp/expandTest/tests/fixtures/advanced-example.js created.
File tmp/expandTest/tests/fixtures/empty.js created.
File tmp/expandTest/tests/fixtures/example.js created.
File tmp/expandTest/tests/fixtures/nested/example.js created.
Running "eco:basePathStringTest" (eco) task
File tmp/basePathStringTest/all.js created.
Running "eco:basePathFunctionTest" (eco) task
File tmp/basePathFunctionTest/all.js created.
Running "eco:amdTest" (eco) task
File tmp/amdTest/tests/fixtures/advanced-example.js created.
File tmp/amdTest/tests/fixtures/empty.js created.
File tmp/amdTest/tests/fixtures/example.js created.
File tmp/amdTest/tests/fixtures/nested/example.js created.
Running "eco:noJstGlobalCheckTest" (eco) task
File tmp/noJstGlobalCheckTest/all.js created.
Running "nodeunit:tests" (nodeunit) task
Testing eco_test.js.......OK
>> 12 assertions passed (6ms)
Done.
The command "grunt" exited with 0.
cache.2
store build cache
Done. Your build exited with 0.

[chenhb-zte]

HI How was the issue of mkdirp fixed on node 6 ? grunt can not run well on node 6.

[cesine]

Hi @chenhb-zte this is how I fixed node 6: I locked the version of grunt to the version which was using mkdirp 0.x a52a148

[chenhb-zte]

Hi @chenhb-zte this is how I fixed node 6: I locked the version of grunt to the version which was using mkdirp 0.x a52a148

THANKS ! it worked well like you said.