Update glide and move testify to require

"glide up" was complaining about testify being a testImport and a main
import. Since we're technically importing it in our application code
(_test.go files), it makes sense to have here.

glide.yaml

@@ -16,6 +16,11 @@ import:
   version: ^0.8.0
 - package: github.com/uber/jaeger-client-go
   version: ^1.6.0
+- package: github.com/stretchr/testify
+  version: ^1.1.3
+  subpackages:
+  - assert
+  - require
 testImport:
 - package: golang.org/x/tools
   version: 3fe2afc9e626f32e91aff6eddb78b14743446865
@@ -34,10 +39,6 @@ testImport:
 - package: github.com/axw/gocov
   subpackages:
   - gocov
-- package: github.com/stretchr/testify
-  version: ^1.1.3
-  subpackages:
-  - assert
 - package: github.com/axw/gocov
 - package: github.com/go-playground/overalls
 - package: github.com/sectioneight/md-to-godoc