Fix instructions for installing shpec

* Use the user/org-prefixed package name
* We don't need the -g, that's part of shpec's configuration

Author: rylnd

_posts/2015-05-05-shpec.md

@@ -86,7 +86,7 @@ end
 ## Installation
 You can either install with bpkg
 {% highlight bash %}
-$ bpkg install -g shpec
+$ bpkg install rylnd/shpec
 {% endhighlight %}
 or with curl
 {% highlight bash %}