Skip fork tests when fork is not available (e.g. Windows)

Author: sodabrew

spec/mysql2/client_spec.rb

@@ -173,8 +173,9 @@ def run_gc
     expect(final_count).to eq(before_count)
   end
 
-
   it "should not close connections when running in a child process" do
+    pending("fork is not available on this platform") unless Process.respond_to?(:fork)
+
     run_gc
     client = Mysql2::Client.new(DatabaseCredentials['root'])