Bump Hermes to 0.7.2

https://github.com/facebook/hermes/releases/tag/v0.7.2 is out so we can bump the pod version 🎉

Question:
Is `~> 0.7.2` too strict? Would `>= 0.7.2` be better?
Also, It doesn't look like we are restricting any version on the trunk?

scripts/react_native_pods.rb

@@ -63,7 +63,7 @@ def use_react_native! (options={})
 
   if hermes_enabled
     pod 'React-Core/Hermes', :path => "#{prefix}/"
-    pod 'hermes-engine', '~> 0.7.1'
+    pod 'hermes-engine', '~> 0.7.2'
     pod 'libevent', :podspec => "#{prefix}/third-party-podspecs/libevent.podspec"
   end
 end