Changed 'hasAttribute' function to 'getAttribute' function in Danger.js

[joeadams0]

I have changed the 'hasAttribute' function to 'getAttribute' in Danger.js. The hasAttribute function was the only thing causing React to not work in IE7 when using the appropriate shims.

I tried to find a shim/sham to accomplish this, but it doesn't seem like it can be accomplished with it.

All tests pass, the lint doesn't, but it doesn't pass in master either.

[syranide]

The devs have explicitly rejected IE7 support, see #2169. While this may be one of the few things that prevents it from actually running, I'm sure there are many inconsistencies and presents major obstacles for further "React improvements". If you want this, fork an IE7 branch of React, or if someone has already made such a thing available. (EDIT: https://www.npmjs.org/package/react-ie)

cc @zpao