Update Cloud GA and Beta versions. (census-instrumentation#1524)

Author: songy23

build.gradle

@@ -156,8 +156,8 @@ subprojects {
         grpcVersion = '1.14.0'
         guavaVersion = '20.0'
         googleAuthVersion = '0.11.0'
-        googleCloudBetaVersion = '0.64.0-beta'
-        googleCloudGaVersion = '1.46.0'
+        googleCloudBetaVersion = '0.68.0-beta'
+        googleCloudGaVersion = '1.50.0'
         log4j2Version = '2.11.1'
         signalfxVersion = '0.0.39'
         springBootVersion = '1.5.15.RELEASE'