Changes for Node 8

1. Start building on travis with Node 8 since it will be LTS soon (it
should slightly speed up builds as well)
2. Add package-lock.json to .gitignore, this is a new npm-generated file
that we won't be submitting to GitHub (it changes almost every time you run
`npm install`).
3. Add package.json to .gitattributes to fix line endings caused by this
npm bug: npm/npm#17161

.gitattributes

@@ -1,2 +1,3 @@
 # Auto detect text files and perform LF normalization
-* text=auto
+* text=auto
+package.json text eol=lf

.gitignore

@@ -24,6 +24,7 @@ Thumbs.db
 /node_modules
 npm-debug.log
 npm-debug.log.*
+package-lock.json
 
 # WebStorm user-specific
 .idea/workspace.xml

.travis.yml

@@ -1,6 +1,6 @@
 language: node_js
 node_js:
-  - "6"
+  - "8"
 sudo: false
 before_script:
   - export DISPLAY=:99.0