Revert "Updated Gemfile [skip ci]"

This reverts commit c6eaaef.

Author: ankane

Gemfile

@@ -5,4 +5,7 @@ gemspec
 gem "rake"
 gem "rake-compiler"
 gem "minitest"
-gem "ruby_memcheck"
+gem "ruby_memcheck", require: false
+
+# https://github.com/ruby/openssl/issues/952
+gem "openssl" if RUBY_PLATFORM =~ /darwin/