Corrected typo from include/webvtt/util.h:81

Replaced 'typ4edef' with 'typedef'
Change #warn to #warning in include/webvtt/util.h

MSVC should not be used if that branch is encountered, and gcc implements
a #warning, so perhaps if the compiler is unknown, #warning will be more
acceptable than #warn
Merge pull request #38 from caitp/issue-38

Syntax error in util.h