Upgrade go-marathon to dd6cbd4.

Fixes a problem with UnreachableStrategy being available now in two
type-incompatible formats (object and string).

We also upgrade the transitive dependency
github.com/donovanhide/eventsource.

glide.lock

@@ -1,5 +1,5 @@
-hash: 6e206389bc4f381387be8b5f0cc5a41224329752654ddb3c2a805adde0333217
-updated: 2017-06-17T14:30:19.890844996+02:00
+hash: 9a62fe4058ef43ed185d96638322dd3d44ae21f7f65fae14c4c6d404876c2872
+updated: 2017-06-28T15:47:14.848940186+02:00
 imports:
 - name: cloud.google.com/go
   version: 2e6a95edb1071d750f6d7db777bf66cd2997af6c
@@ -178,7 +178,7 @@ imports:
   - store/etcd
   - store/zookeeper
 - name: github.com/donovanhide/eventsource
-  version: fd1de70867126402be23c306e1ce32828455d85b
+  version: 441a03aa37b3329bbb79f43de81914ea18724718
 - name: github.com/eapache/channels
   version: 47238d5aae8c0fefd518ef2bee46290909cf8263
 - name: github.com/eapache/queue
@@ -201,7 +201,7 @@ imports:
 - name: github.com/fatih/color
   version: 9131ab34cf20d2f6d83fdc67168a5430d1c7dc23
 - name: github.com/gambol99/go-marathon
-  version: 15ea23e360abb8b25071e677aed344f31838e403
+  version: dd6cbd4c2d71294a19fb89158f2a00d427f174ab
 - name: github.com/ghodss/yaml
   version: 73d445a93680fa1a78ae23a5839bad48f32ba1ee
 - name: github.com/go-ini/ini