Don't clobber stacktrace, just let the AttributeError raise

[asottile]

This was hiding the underlying error in a stacktrace of ours.

The new line 67 will raise anyway if the attribute is not there. getattr unlike dict#get raises when not present.

[mjbryant]

👍 . This was cribbed from the bravado_decorators internal repo. You might want to change that, too, or this problem will probably happen again.

[asottile]

and that was copied from gluapy.factory apparently >.< where does the copypasta end?

[asottile]

also an internal package it appears