Change version to 1.27.0 (#3340)

[skip ci] Skipping Travis. Version number change only
diff --git a/version.go b/version.go
index b35c2ed..cf19382 100644
--- a/version.go
+++ b/version.go
@@ -19,4 +19,4 @@
 package grpc
 
 // Version is the current grpc version.
-const Version = "1.27.0-dev"
+const Version = "1.27.0"