Update release date

Author: kimwalisch

CHANGELOG.md

@@ -2,7 +2,7 @@
 
 This is a list of notable changes to libdivide.
 
-## [3.0](https://github.com/ridiculousfish/libdivide/releases/tag/v3.0) - not yet released
+## [3.0](https://github.com/ridiculousfish/libdivide/releases/tag/v3.0) - 2019-10-16
 * BREAKING
   * ```libdivide.h``` now requires C++11 or later
 * BUG FIXES