Update C++ version.

Author: jonsimantov

cpp_sdk_version.json

@@ -1,5 +1,5 @@
 {
-  "released": "12.6.0",
-  "stable": "12.6.0",
-  "head": "12.6.0"
+  "released": "12.7.0",
+  "stable": "12.7.0",
+  "head": "12.7.0"
 }