Stop linting on npm install

It's annoying to run the linter on npm install, because it slows down the
react-sdk and riot-web builds.

The fact that `npm install` runs `prepublish` is going to be changed in npm 4
(see npm/npm#14290), but for now this is the best bet.

.travis.yml

@@ -1,3 +1,6 @@
 language: node_js
 node_js:
     - node # Latest stable version of nodejs.
+script:
+    - npm run lint
+    - npm run test

package.json

@@ -12,7 +12,7 @@
     "dist": "npm run build",
     "watch": "watchify --exclude olm browser-index.js -o dist/browser-matrix-dev.js -v",
     "lint": "eslint --max-warnings 122 src spec",
-    "prepublish": "npm run lint && npm run build && git rev-parse HEAD > git-revision.txt"
+    "prepublish": "npm run build && git rev-parse HEAD > git-revision.txt"
   },
   "repository": {
     "url": "https://github.com/matrix-org/matrix-js-sdk"