single quote char (ASCII 39) causing failures with GCS

[kevmoo]

Seems this is the root cause of the following

dart-lang/pub#1666
dart-lang/pub-dev#230

Solution: remove single quote from set of considered boundary characters

[kevmoo]

Can't figure out what this change dart-lang/sdk@ebffa49

Which included this range of changes 0.11.3+9...0.11.3+13 would cause this behavior to be exposed