chore: add package-lock.json and prettier (#131)

## Description

This PR checks in `package-lock.json`, which is recommended to be checked in by npm.

This PR also adds code formatting with Prettier. This is accomplished by adding a `npm run pretty` command which anyone can run to format the source code and tests.

It is also recommended that PrettierCI be added to this repo to enforce code formatting.

Author: frederickfogerty

.prettierignore

@@ -0,0 +1,4 @@
+CHANGELOG.md
+package.json
+package-lock.json
+dist

.prettierrc

@@ -0,0 +1 @@
+singleQuote: true

.travis.yml

@@ -14,3 +14,8 @@ addons:
       - ubuntu-toolchain-r-test
     packages:
       - g++-4.8
+
+branches:
+  only:
+    - master
+    - /release.*/