don't remove anonymous functions from stack trace

TraceKit's stacktrace regex for Chrome didn't match anonymous functions, so all anonymous functions in the stacktrace were being removed before reporting to Sentry.  This caused errors to be attributed to the wrong files, and was generally extremely confusing.  This change updates the regex to not *require* a function name be present in the stacktrace.

see #289 

Hmm, this test will be brittle since it's tied specifically to how it's handled by Chrome. Could we block an exception object instead?