spec/ruby/optional/capi/io_spec.rb: speling fics

* spec/ruby/optional/capi/io_spec.rb: speling: s/writeable/writable/

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60191 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

spec/ruby/optional/capi/io_spec.rb

@@ -234,7 +234,7 @@ describe "C-API IO function" do
     end
   end
 
-  describe "rb_io_wait_writeable" do
+  describe "rb_io_wait_writable" do
     it "returns false if there is no error condition" do
       @o.rb_io_wait_writable(@w_io).should be_false
     end