Fix to pass arguments to standard-markdown

If you do not specify an argument, the `standard-markdown` will fail.
zeke/standard-markdown#25
This is an interim fix.

package.json

@@ -60,7 +60,7 @@
     "full-ci": "npm run lint && npm run coverage",
     "coverage": "istanbul cover -i 'lib/**' -x '**/__tests__/**' test.js",
     "coveralls": "coveralls < coverage/lcov.info",
-    "lint": "standard && standard-markdown",
+    "lint": "standard && standard-markdown *.md docs/*.md",
     "test-find": "find ./lib/**/__tests__ -name *.test.js | xargs mocha",
     "test": "npm run lint && npm run unit",
     "unit": "node test.js"