Removed the badge of appveyor.

Author: hsbt

README.rdoc

@@ -3,7 +3,7 @@
 home :: https://github.com/ruby/rake
 bugs :: https://github.com/ruby/rake/issues
 docs :: https://ruby.github.io/rake
-build status :: {<img src="https://travis-ci.org/ruby/rake.svg?branch=master" alt="travis-ci">}[https://travis-ci.org/ruby/rake] {<img src="https://ci.appveyor.com/api/projects/status/github/ruby/rake?branch=master&svg=true" alt="appveyor">}[https://ci.appveyor.com/project/ruby/rake]
+build status :: {<img src="https://travis-ci.org/ruby/rake.svg?branch=master" alt="travis-ci">}[https://travis-ci.org/ruby/rake]
 
 == Description