Initialize go modules

Author: jmrodri

go.mod

@@ -0,0 +1,13 @@
+module github.com/operator-framework/operator-lib
+
+go 1.13
+
+require (
+	github.com/stretchr/testify v1.5.1
+	k8s.io/api v0.18.2
+	k8s.io/apimachinery v0.18.2
+	k8s.io/client-go v12.0.0+incompatible
+	sigs.k8s.io/controller-runtime v0.6.0
+)
+
+replace k8s.io/client-go => k8s.io/client-go v0.18.2