🛠 Added .travis.yml and gscan tests (#470)

- Add gscan dependency & travis.yml file, so that we can run gscan as a test for this repo
- This check tells us whether or not the theme is valid & compatible with Ghost according to gscan
- We recommend that all themes do this!

.travis.yml

@@ -0,0 +1,6 @@
+language: node_js
+sudo: false
+node_js:
+  - "8"
+
+

package.json

@@ -13,7 +13,8 @@
     },
     "scripts": {
         "dev": "gulp",
-      "zip": "gulp zip"
+        "zip": "gulp zip",
+        "test": "gscan ."
     },
     "author": {
         "name": "Ghost Foundation",
@@ -41,6 +42,7 @@
     "devDependencies": {
         "autoprefixer": "6.3.6",
         "cssnano": "3.7.1",
+        "gscan": "^2.0.0",
         "gulp": "3.9.1",
         "gulp-livereload": "3.8.1",
         "gulp-postcss": "6.1.1",