golangci-lint: enable ginkgolinter

The ginkgolinter can detect sub-optimal usage of gomega assertions, for
example:

   Expect(len(x)).To(Equal(0)) // should be: Expect(x).To(BeEmpty())

.golangci.yaml

@@ -20,6 +20,7 @@ issues:
 linters:
   disable-all: true
   enable: # please keep this alphabetized
+    - ginkgolinter
     - gocritic
     - ineffassign
     - logcheck