Bump development version to 1.9.0

Stable releases for 1.8.x will be made off of the release/1.8.x branch.
Main will represent the next minor version. When ready for a release a new release branch will
be created for the version.

version/VERSION

@@ -1 +1 @@
-1.8.6
+1.9.0

version/version.go

@@ -19,7 +19,7 @@ var (
 	// A pre-release marker for the version can also be specified (e.g -dev). If this is omitted
 	// The main version number that is being run at the moment.
 
-	Version = "1.8.6"
+	Version = "1.9.0"
 
 	// A pre-release marker for the version. If this is "" (empty string)
 	// then it means that it is a final release. Otherwise, this is a pre-release