postgresql 9.6beta2 (devel) (#2497)

- [x] Have you followed the guidelines in our [Contributing](https://github.com/Homebrew/homebrew-core/blob/master/.github/CONTRIBUTING.md) document?
- [x] Have you checked to ensure there aren't other open [Pull Requests](https://github.com/Homebrew/homebrew-core/pulls) for the same formula update/change?
- [x] Have you built your formula locally prior to submission with `brew install <formula>` (where `<formula>` is the name of the formula you're submitting)?
- [x] Does your submission pass `brew audit --strict --online <formula>` (after doing `brew install <formula>`)?

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June 23rd 2016 PostgreSQL announced next beta for upcoming 9.6 release: https://www.postgresql.org/about/news/1677/

Link to archive and checksum is https://www.postgresql.org/ftp/source/v9.6beta2/

Formula/postgresql.rb

@@ -11,9 +11,9 @@ class Postgresql < Formula
   end
 
   devel do
-    url "https://ftp.postgresql.org/pub/source/v9.6beta1/postgresql-9.6beta1.tar.gz"
-    version "9.6beta1"
-    sha256 "14539ea9cba8c588b46bb746f8ab999de4093464b8fc16747b8002ca5f93787d"
+    url "https://ftp.postgresql.org/pub/source/v9.6beta2/postgresql-9.6beta2.tar.gz"
+    version "9.6beta2"
+    sha256 "fe4b75548ebccea7140f3285f2a4b118fa0651f18dd1f63a6c41ef9046042cb1"
   end
 
   option "32-bit"