Incremented gem version to 3.2.0.2

This version is to push a fix for gems containing files that were not
world-readable as they should be (issue #2853).

ruby/google-protobuf.gemspec

 Gem::Specification.new do |s|
   s.name        = "google-protobuf"
-  s.version     = "3.2.0.1"
+  s.version     = "3.2.0.2"
   s.licenses    = ["BSD-3-Clause"]
   s.summary     = "Protocol Buffers"
   s.description = "Protocol Buffers are Google's data interchange format."