Travis: Don't install npm in the before_install hook.

nodejs/node-gyp#564 suggests this might fix the io.js build.

Author: papandreou

.travis.yml

@@ -3,7 +3,7 @@ node_js:
   - "0.10"
   - "0.12"
   - "iojs-v2.3.1"
-before_install: "sudo apt-get update && sudo apt-get install -y libcairo2-dev libjpeg8-dev libgif-dev optipng pngcrush pngquant libpango1.0-dev graphicsmagick libjpeg-turbo-progs inkscape && npm install -g npm && npm cache clean"
+before_install: "sudo apt-get update && sudo apt-get install -y libcairo2-dev libjpeg8-dev libgif-dev optipng pngcrush pngquant libpango1.0-dev graphicsmagick libjpeg-turbo-progs inkscape"
 script: "npm run-script travis"
 after_success: "<coverage/lcov.info ./node_modules/coveralls/bin/coveralls.js"