yaml-cpp: apply upstream patch to avoid installation of gtest

Closes #33751.

Signed-off-by: Chongyu Zhu <i@lembacon.com>

Formula/yaml-cpp.rb

@@ -3,6 +3,7 @@ class YamlCpp < Formula
   homepage "https://github.com/jbeder/yaml-cpp"
   url "https://github.com/jbeder/yaml-cpp/archive/yaml-cpp-0.6.2.tar.gz"
   sha256 "e4d8560e163c3d875fd5d9e5542b5fd5bec810febdcba61481fe5fc4e6b1fd05"
+  revision 1
 
   bottle do
     cellar :any
@@ -14,6 +15,14 @@ class YamlCpp < Formula
 
   depends_on "cmake" => :build
 
+  # Upstream commit from Sep 3 2018 "Improvements to CMake buildsystem"
+  # which fixes the unexpected installation of Google Test.
+  # See https://github.com/jbeder/yaml-cpp/issues/539
+  patch do
+    url "https://github.com/jbeder/yaml-cpp/commit/5e79f5eed3d86125468681116e92814d2cf40067.patch?full_index=1"
+    sha256 "52da989f0dcaca68ae9ee6334155954639506e16cbe3b9bd007dace9e171e4bd"
+  end
+
   needs :cxx11
 
   def install