Bump version to 0.6.3.1

This version bump is to add a tag to the repository, the Haskell
source code of hpc-codecov is identical to 0.6.3.0.

Author: 8c6794b6

hpc-codecov.cabal

@@ -1,6 +1,6 @@
 cabal-version:       2.0
 name:                hpc-codecov
-version:             0.6.3.0
+version:             0.6.3.1
 synopsis:            Generate reports from hpc data
 license:             BSD3
 license-file:        LICENSE