[ruby/securerandom] Bump version to 0.2.1

https://github.com/ruby/securerandom/commit/5bfe7d6c16

lib/securerandom.gemspec

@@ -1,6 +1,6 @@
 Gem::Specification.new do |spec|
   spec.name          = "securerandom"
-  spec.version       = "0.2.0"
+  spec.version       = "0.2.1"
   spec.authors       = ["Tanaka Akira"]
   spec.email         = ["akr@fsij.org"]