add electron 3 build

Ref galkahana#344

.travis.yml

@@ -21,6 +21,7 @@ env:
   - NODE_NVM_VERSION="10.8.0"
   - ELECTRON_VERSION="1.8.7" NODE_NVM_VERSION="8.11.1"
   - ELECTRON_VERSION="2.0.7" NODE_NVM_VERSION="8.11.1"
+  - ELECTRON_VERSION="3.0.7" NODE_NVM_VERSION="8.11.1"
   - MUSL=true NODE_NVM_VERSION="8.11.1"
   - MUSL=true NODE_NVM_VERSION="9.11.1"
   - MUSL=true NODE_NVM_VERSION="10.8.0"
@@ -34,6 +35,7 @@ before_install:
   export npm_config_target_arch=x64;
   export npm_config_disturl=https://atom.io/download/electron;
   export npm_config_runtime=electron;
+  export npm_config_build_from_source=true
   fi
 - COMMIT_MESSAGE=$(git show -s --format=%B $TRAVIS_COMMIT | tr -d '\n')
 - PUBLISH_BINARY=false
@@ -55,6 +57,6 @@ install:
 script:
 - ./node_modules/.bin/node-pre-gyp package testpackage $EXTRA_NODE_PRE_GYP_FLAGS
 - npm test
-- if [[ "${PUBLISH_BINARY}" == "true" ]]; then ./node_modules/.bin/node-pre-gyp unpublish 
+- if [[ "${PUBLISH_BINARY}" == "true" ]]; then ./node_modules/.bin/node-pre-gyp unpublish
   publish $EXTRA_NODE_PRE_GYP_FLAGS; rm -rf {build,binding}; ./node_modules/.bin/node-pre-gyp install $EXTRA_NODE_PRE_GYP_FLAGS; npm test;
   fi

appveyor.yml

@@ -6,7 +6,7 @@ environment:
   matrix:
     - nodejs_version: 4
       platform: x64
-      msvs_toolset: 12      
+      msvs_toolset: 12
     - nodejs_version: 5
       platform: x64
     - nodejs_version: 6
@@ -20,6 +20,11 @@ environment:
     - nodejs_version: 10
       platform: x64
     # electron
+    - nodejs_version: 8
+      platform: x64
+      NODE_RUNTIME: electron
+      NODE_RUNTIME_VERSION: 3.0.7
+      TOOLSET_ARGS: --dist-url=https://atom.io/download/electron
     - nodejs_version: 8
       platform: x64
       NODE_RUNTIME: electron
@@ -37,4 +42,4 @@ install:
 
 build: OFF
 test: OFF
-deploy: OFF 
+deploy: OFF