fix: Vulcand dependency version : vulcand/predicate

`vulcand/predicate` is used by:
- `github.com/vulcand/oxy` (no dependencies manager)
- `github.com/vulcand/route` (used by `github.com/vulcand/vulcand`)

`github.com/vulcand/vulcand` (Godeps) required a old version `cb0bff91a7ab7cf7571e661ff883fc997bc554a3`.

`19b9dde14240d94c804ae5736ad0e1de10bf8fe6` is the only commit before `cb0bff91a7ab7cf7571e661ff883fc997bc554a3`.

refs:
- https://github.com/vulcand/vulcand/blob/42492a3a85e294bdbdd1bcabb8c12769a81ea284/Godeps/Godeps.json
- https://github.com/vulcand/predicate/commits/master
- vulcand/predicate@19b9dde

glide.yaml

@@ -61,6 +61,8 @@ import:
   version: 42492a3a85e294bdbdd1bcabb8c12769a81ea284
   subpackages:
   - plugin/rewrite
+- package: github.com/vulcand/predicate
+  version: 19b9dde14240d94c804ae5736ad0e1de10bf8fe6
 - package: github.com/xenolf/lego
   version: 5dfe609afb1ebe9da97c9846d97a55415e5a5ccd
   subpackages: