Fixed the version range for sinon-chai.

Fix for this bug:
```
$ ./reset.sh --verbose
---- Resetting / Initializing Appium ----
RESETTING NPM
* Installing new or updated NPM modules (including devDeps)
npm http GET https://registry.npmjs.org/sinon-chai
npm http 304 https://registry.npmjs.org/sinon-chai
npm ERR! Error: No compatible version found: sinon-chai@'^2.5.0'
npm ERR! Valid install targets:
npm ERR! ["1.0.0","1.1.0","1.2.0","1.2.1","1.2.2","1.3.0","1.3.1","2.0.0","2.0.1","2.1.0","2.1.1","2.1.2","2.2.0","2.3.0","2.3.1","2.4.0","2.5.0"]
npm ERR!     at installTargetsError (/usr/local/lib/node_modules/npm/lib/cache.js:685:10)
npm ERR!     at /usr/local/lib/node_modules/npm/lib/cache.js:607:10
npm ERR!     at saved (/usr/local/lib/node_modules/npm/node_modules/npm-registry-client/lib/get.js:138:7)
npm ERR!     at Object.oncomplete (fs.js:107:15)
npm ERR! If you need help, you may report this log at:
npm ERR!     <http://github.com/isaacs/npm/issues>
npm ERR! or email it to:
npm ERR!     <npm-@googlegroups.com>

npm ERR! System Darwin 13.1.0
npm ERR! command "node" "/usr/local/bin/npm" "install" "."
npm ERR! cwd /Users/paymand/src/appium
npm ERR! node -v v0.10.5
npm ERR! npm -v 1.2.18
npm ERR! 
npm ERR! Additional logging details can be found in:
npm ERR!     /Users/paymand/src/appium/npm-debug.log
npm ERR! not ok code 0
---- FAILURE: reset.sh exited with status 1 ----
```