Removed last "/" from mesosphere-public-repo URL

Small change. mesoshpere-maven-public does not allow "//", so I can't build chronos.

    $ curl -v http://s3.amazonaws.com/mesosphere-maven-public//org/apache/mesos/mesos/0.14.1-SNAPSHOT/maven-metadata.xml
    * About to connect() to s3.amazonaws.com port 80 (#0)
    *   Trying 207.171.189.80...
    * connected
    * Connected to s3.amazonaws.com (207.171.189.80) port 80 (#0)
    > GET /mesosphere-maven-public//org/apache/mesos/mesos/0.14.1-SNAPSHOT/maven-metadata.xml HTTP/1.1
    > User-Agent: curl/7.24.0 (x86_64-apple-darwin12.0) libcurl/7.24.0 OpenSSL/0.9.8x zlib/1.2.5
    > Host: s3.amazonaws.com
    > Accept: */*
    >
    < HTTP/1.1 404 Not Found
    < x-amz-request-id: F882C9F5DB8112BF
    < x-amz-id-2: YqMbcbQw/QrzsKgpzrMOPgpur3dp8zOlHghDSgp8XfgyOWQDdjxNRazD8hqMdSKw
    < Content-Type: application/xml
    < Transfer-Encoding: chunked
    < Date: Tue, 06 Aug 2013 00:23:50 GMT
    < Server: AmazonS3