merge https://github.com/facebook/folly/pull/88

Summary:
merge https://github.com/facebook/folly/pull/88, missing install header

Looks like fbthrift build needs this

Test Plan: watch jenkins build still works

Reviewed By: ckwalsh@fb.com

Subscribers: doug, njormrod

FB internal diff: D1563651

folly/Makefile.am

@@ -175,6 +175,7 @@ nobase_follyinclude_HEADERS = \
 	Uri.h \
 	Uri-inl.h \
 	Varint.h \
+	VersionCheck.h \
 	wangle/Executor.h \
 	wangle/Future-inl.h \
 	wangle/Future.h \