Replace yarn with npm

The recommended way of installing nin is by npm link, so using yarn
doesn't relly make sense. (There is no proper yarn alternative for npm
link -- yarn link does something else). At any rate, npm is good again
now, so making the switch isn't too bad.

.travis.yml

@@ -4,9 +4,8 @@ node_js:
 notifications:
   email: false
 install:
-  - npm install -g yarn
-  - yarn
-  - cd nin/frontend && yarn && cd -
+  - npm install
+  - cd nin/frontend && npm install && cd -
 script:
   - cd nin/backend && ../../node_modules/.bin/eslint .
   - cd ../frontend && make lint

Makefile

@@ -1,6 +1,6 @@
 .PHONY: all
 all:
-	yarn start
+	npm start
 
 .PHONY: publish
 publish: all

README.md

@@ -105,8 +105,7 @@ Expect to render maybe a frame or two per second.
 
 ## Setup
 
-You will need to have node and yarn installed.
-Yarn installation guide is available [here](https://yarnpkg.com/en/docs/install).
+You will need to have node installed.
 
 Running `make` in the nin folder will build and compile the entire project.
 Running `npm link` will add nin to your node binaries path, making it available globally.
@@ -241,9 +240,9 @@ To be able to publish you need access to the `ninjadev` user on npm whose passwo
 
 ## Notes on working in windows
 
-The prerequisites remain the same, you at least need Yarn and Node.
+The prerequisites remain the same, you at least need Node.
 
-To build and compile the entire project, for now, you need only run `yarn start` in the root of the nin-repo.
+To build and compile the entire project, for now, you need only run `npm start` in the root of the nin-repo.
 To run nin without linking up through npm you can replace the `nin`-command with `node path-to-ninrepo/nin/backend/nin`.
 E.g. when you are in a project folder of a demo, and you want to run it with your freshly compiled nin directly, you can run `node path-to-ninrepo/nin/backend/nin run` instead of `nin run`.
 

nin/frontend/Makefile

@@ -1,11 +1,11 @@
 .PHONY: all
 all:
-	yarn start
+	npm start
 
 .PHONY: run
 run:
-	yarn run webpack-watch
+	npm run webpack-watch
 
 .PHONY: lint
 lint:
-	yarn lint
+	npm run lint

nin/frontend/package.json

@@ -37,7 +37,7 @@
     "node": ">=4.0.0"
   },
   "scripts": {
-    "start": "yarn install && yarn build",
+    "start": "npm install && npm build",
     "build": "webpack -p",
     "webpack-watch": "webpack --watch --display-error-details",
     "lint": "eslint app",