Few more fixes to the Ruby installation.

-) properly depending on libraries.
-) adding an independent 'loader' class to use instead of require 'grpc/grpc'.
diff --git a/build.yaml b/build.yaml
index e9dd788..52d4048 100644
--- a/build.yaml
+++ b/build.yaml
@@ -2642,3 +2642,9 @@
   - gpr
   - boringssl
   - z
+ruby_gem:
+  deps:
+  - grpc
+  - gpr
+  - boringssl
+  - z