Generate properly encoded javadoc url

This is a follow-up to https://github.com/clojure-emacs/cider/pull/910.

For an example of a url that wouldn't load without this fix, see the cider-doc view for Integer/parseInt.
(browse-url "http://docs.oracle.com/javase/7/docs/api/java/lang/Integer.html#parseInt(java.lang.String, int)")
does not work on OS X. Emacs issues the command
```
open 'http://docs.oracle.com/javase/7/docs/api/java/lang/Integer.html#parseInt(java.lang.String, int)'
```
which does not work correctly: you are sent to http://docs.oracle.com/javase/7/docs/api/java/lang/Integer.html%23parseInt(java.lang.String,%20int)