Fix copy-pasta in the gemspec

Signed-off-by: Tim Smith <tsmith@chef.io>

mixlib-versioning.gemspec

@@ -9,7 +9,7 @@ Gem::Specification.new do |spec|
   spec.authors       = ["Seth Chisamore", "Christopher Maier"]
   spec.description   = "General purpose Ruby library that allows you to parse, compare and manipulate version strings in multiple formats."
   spec.summary       = spec.description
-  s.email            = "info@chef.io"
+  spec.email         = "info@chef.io"
   spec.homepage      = "https://github.com/chef/mixlib-versioning"
   spec.license       = "Apache-2.0"