update download url

src/en/guide/gettingStarted/downloadingAndInstalling.gdoc

@@ -1,10 +1,10 @@
-The first step to getting up and running with Grails is to install the distribution. 
+The first step to getting up and running with Grails is to install the distribution.
 
 The best way to install Grails on *nix systems is with the [GVM tool|http://gvmtool.net] which greatly simplifies installing and managing multiple Grails versions.
 
 For manual installation follow these steps:
 
-* "Download":http://grails.org/Download a binary distribution of Grails and extract the resulting zip file to a location of your choice
+* "Download":https://github.com/grails/grails-core/releases a binary distribution of Grails and extract the resulting zip file to a location of your choice
 * Set the GRAILS_HOME environment variable to the location where you extracted the zip
 ** On Unix/Linux based systems this is typically a matter of adding something like the following @export GRAILS_HOME=/path/to/grails@ to your profile
 ** On Windows this is typically a matter of setting an environment variable under @My Computer/Advanced/Environment Variables@
@@ -16,4 +16,3 @@ If Grails is working correctly you should now be able to type @grails -version@
 
 bc.
 Grails version: 3.0.0
-