Update feedx.gemspec

Ruby 0.13.0 was never released.

But v0.13.0 Git tag was created (old one).

So skipping v0.13.0 version for ruby to keep them synced between ruby and go.

feedx.gemspec

@@ -1,6 +1,6 @@
 Gem::Specification.new do |s|
   s.name          = 'feedx'
-  s.version       = '0.13.0'
+  s.version       = '0.13.1'
   s.authors       = ['Black Square Media Ltd']
   s.email         = ['[email protected]']
   s.summary       = %(Exchange data between components via feeds)