Correct spelling of GitHub (#87)

Author: fulldecent

template.erb

@@ -38,7 +38,7 @@
         otherLinks: [{
             key: 'Participate',
             data: [{
-                      value: 'We are on Github.',
+                      value: 'We are on GitHub.',
                       href: 'https://github.com/w3c/webappsec-subresource-integrity'
                   }, {
                       value: 'File a bug.',