Start 1.16.0 development cycle (#4803)

diff --git a/build.gradle b/build.gradle
index e4d6140..2297bed 100644
--- a/build.gradle
+++ b/build.gradle
@@ -53,7 +53,7 @@
     idea.module.inheritOutputDirs = true
 
     group = "io.grpc"
-    version = "1.15.0-SNAPSHOT" // CURRENT_GRPC_VERSION
+    version = "1.16.0-SNAPSHOT" // CURRENT_GRPC_VERSION
 
     sourceCompatibility = 1.7
     targetCompatibility = 1.7