Adapt to support PDF.js v1.0.907

... as per #86.

Tested with:
 * Iceweasel 31.2.0 (Shipped with Debian, built on top of Firefox ESR) - ships with PDF.js v1.0.68
 * Firefox 31.3.0 (current ESR a.k.a. Extended Support Release) - ships with PDF.js v1.0.68
 * Firefox 34.0.5 (current stable) - ships with PDF.js v1.0.712
 * Firefox 34.0.5 (current beta - yes, it's the same as stable, just released) - ships with PDF.js v1.0.712
 * Firefox 35.0a2 (developer edition a.k.a. aurora a.k.a. alpha) - ships with PDF.js v1.0.907

According to tests, all involved PDF.js versions are now fully supported.

> That's why `tryIt` and the `setTimeout` closure need the fat arrow, but this method does not.

I don't think that's how fat arrows work in CoffeeScript. See the short test below:

`ScopeTest.coffee`:

```
class ScopeTest
       	
  test: (arg) => console.log arg, "Works!"

  fatMethod: =>
    testFunction = => @test("Fat")
    testFunction()

  thinMethod: ->
    testFunction = => @test("Thin")
    testFunction()


testObject = new ScopeTest()
test = testObject.fatMethod
test()
test = testObject.thinMethod
test()
```

Output:

```
Fat Works!
TypeError: Object #<Object> has no method 'test'
  at /tmp/fattest.coffee:10:24
  at ScopeTest.thinMethod (/tmp/fattest.coffee:11:5)
  at Object.<anonymous> (/tmp/fattest.coffee:18:1)
  at Object.<anonymous> (/tmp/fattest.coffee:1:1)
  at Module._compile (module.js:456:26)
```

My interpretation: you need a full chain of fat arrows (down from the object scope to the function) for this to work.