replace gomega with require in prometheus output client tests

Signed-off-by: Robert Sullivan <rsullivan@pivotal.io>

Gopkg.lock

@@ -821,27 +821,6 @@
   revision = "eee57a3ac4174c55924125bb15eeeda8cffb6e6f"
   version = "v1.0.7"
 
-[[projects]]
-  digest = "1:c8f0c8c28c9c1c51db72d0e7f04797cfe5d0d50528274099b6b2d6c314db7f97"
-  name = "github.com/onsi/gomega"
-  packages = [
-    ".",
-    "format",
-    "internal/assertion",
-    "internal/asyncassertion",
-    "internal/oraclematcher",
-    "internal/testingtsupport",
-    "matchers",
-    "matchers/support/goraph/bipartitegraph",
-    "matchers/support/goraph/edge",
-    "matchers/support/goraph/node",
-    "matchers/support/goraph/util",
-    "types",
-  ]
-  pruneopts = ""
-  revision = "65fb64232476ad9046e57c26cd0bff3d3a8dc6cd"
-  version = "v1.4.3"
-
 [[projects]]
   digest = "1:5d9b668b0b4581a978f07e7d2e3314af18eb27b3fb5d19b70185b7c575723d11"
   name = "github.com/opencontainers/go-digest"
@@ -1589,7 +1568,6 @@
     "github.com/nats-io/gnatsd/server",
     "github.com/nats-io/go-nats",
     "github.com/nsqio/go-nsq",
-    "github.com/onsi/gomega",
     "github.com/openzipkin/zipkin-go-opentracing",
     "github.com/openzipkin/zipkin-go-opentracing/thrift/gen-go/zipkincore",
     "github.com/prometheus/client_golang/prometheus",