Merge pull request #336 from rogpeppe/025-go.mod

add go.mod file
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..1934e87
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,5 @@
+module "gopkg.in/yaml.v2"
+
+require (
+	"gopkg.in/check.v1" v0.0.0-20161208181325-20d25e280405
+)