Fixes errors produced by dep 0.5.0.

Recent version of dep - 0.5.0 produces errors on `dep status`:
```
◦ dep status
Gopkg.lock is out of sync with imports and/or Gopkg.toml. Run `dep check` for details.
PROJECT  MISSING PACKAGES
input-digest mismatch
```

This commit updates `Gopkg.lock` to recent dep format

I essentially ran `dep ensure`.

Gopkg.lock

@@ -2,26 +2,32 @@
 
 
 [[projects]]
+  digest = "1:a2c1d0e43bd3baaa071d1b9ed72c27d78169b2b269f71c105ac4ba34b1be4a39"
   name = "github.com/davecgh/go-spew"
   packages = ["spew"]
+  pruneopts = "UT"
   revision = "346938d642f2ec3594ed81d874461961cd0faa76"
   version = "v1.1.0"
 
 [[projects]]
+  digest = "1:0028cb19b2e4c3112225cd871870f2d9cf49b9b4276531f03438a88e94be86fe"
   name = "github.com/pmezard/go-difflib"
   packages = ["difflib"]
+  pruneopts = "UT"
   revision = "792786c7400a136282c1664665ae0a8db921c6c2"
   version = "v1.0.0"
 
 [[projects]]
+  digest = "1:f85e109eda8f6080877185d1c39e98dd8795e1780c08beca28304b87fd855a1c"
   name = "github.com/stretchr/testify"
   packages = ["assert"]
+  pruneopts = "UT"
   revision = "12b6f73e6084dad08a7c6e575284b177ecafbc71"
   version = "v1.2.1"
 
 [solve-meta]
   analyzer-name = "dep"
   analyzer-version = 1
-  inputs-digest = "dbc03d7c9dd4e54b6993c8ece59c3174becb58bd828e500cf8ad825e340278c4"
+  input-imports = ["github.com/stretchr/testify/assert"]
   solver-name = "gps-cdcl"
   solver-version = 1