update gem version to 4.0.6

Author: prettycoder

lib/appoptics_apm/version.rb

@@ -8,7 +8,7 @@ module AppOpticsAPM
   module Version
     MAJOR = 4
     MINOR = 0
-    PATCH = 5
+    PATCH = 6
 
     STRING = [MAJOR, MINOR, PATCH].compact.join('.')
   end