Update import paths for changes to blueprint

Blueprint has been modified to include a canonical import path,
update soong to match.

Change-Id: If29d31afbf3bf2e6364961a66456fa5f8f738455
diff --git a/common/module.go b/common/module.go
index 9bdd7c1..6b2dfb4 100644
--- a/common/module.go
+++ b/common/module.go
@@ -15,7 +15,7 @@
 package common
 
 import (
-	"blueprint"
+	"github.com/google/blueprint"
 	"path/filepath"
 )
 
@@ -135,7 +135,7 @@
 //
 //     import (
 //         "android/soong/common"
-//         "blueprint"
+//         "github.com/google/blueprint"
 //     )
 //
 //     type myModule struct {