Update to latest acorn

[SimenB]

Currently, eslint pulls in 2 versions of acorn because of this dep.

$ npm ls acorn
...
└─┬ eslint@3.7.1
  └─┬ espree@3.3.2
    ├── acorn@4.0.3
    └─┬ acorn-jsx@3.0.1
      └── acorn@3.3.0

[wtgtybhertgeghgtwtg]

Alternatively, remove auto-inject so acorn is not required at all.