Update Changes for version 1.21

Author: pali

Changes

@@ -1,3 +1,8 @@
+1.21 2019-02-27
+ - Fix skipping test t/14destruct.t
+ - Revert "MySQL bug #93276 is fixed in 8.0.15"
+   (https://github.com/gooddata/DBD-MariaDB/issues/137)
+
 1.20 2019-02-22
  - Fix compilation on Windows
  - Fix tests for MariaDB 10.2.20+, 10.3.12+ and 10.4.1+