_getTestFramework is checking for incorrect mocha package

[andrewfan]

ember-cli-mocha package is deprecated thus here https://github.com/ember-cli/ember-exam/blob/master/lib/commands/exam.js#L136 we should also check for ember-mocha dependency

[choheekim]

looking into it!
#472

[step2yeung]

@andrewfan looks like #472 is merged! Have you had a chance to verify this is good?