Add go-version-file option (#62)

__tests__/data/go.mod

@@ -0,0 +1,12 @@
+module example.com/mymodule
+
+go 1.14
+
+require (
+	example.com/othermodule v1.2.3
+	example.com/thismodule v1.2.3
+	example.com/thatmodule v1.2.3
+)
+
+replace example.com/thatmodule => ../thatmodule
+exclude example.com/thismodule v1.3.0