Require the latest version of npm

The npm that ships with 0.10 is 1.2.x and it is riddled with
race conditions.

.travis.yml

@@ -1,18 +1,14 @@
 sudo: false
 language: php
-cache:
-  directories:
-  - node_modules
 php:
 - '5.6'
 - '5.5'
 - '5.4'
 
 before_install:
-  - npm cache clean
-  - npm prune
+  - npm install -g npm@latest
   - npm install -g bower gulp jscs
-  - npm update
+  - npm install
   - pyrus install pear/PHP_CodeSniffer
   - phpenv rehash