Update module files BUT enabling modules breaks the build.

The new updates to golang modules ensure that this code generation
solution just got a lot more painful, as now each generated subpackage
needs its own go-mod file autogenerated, it seems.

go.mod

@@ -1,7 +1,11 @@
-module github.com/go-fed/activity
+module go-fed/activity
+
+go 1.12
 
 require (
+	github.com/dave/jennifer v1.3.0
+	github.com/go-fed/activity v0.4.0
 	github.com/go-fed/httpsig v0.1.0
 	github.com/go-test/deep v1.0.1
-	golang.org/x/time v0.0.0-20180412165947-fbb02b2291d2
+	github.com/golang/mock v1.2.0
 )

go.sum

@@ -1,10 +1,15 @@
-github.com/go-fed/httpsig v0.1.0 h1:clkeIoBexg4Fmc8u5mneN5nFPdisCWHATTB8mMsP+/E=
+github.com/dave/jennifer v1.3.0 h1:p3tl41zjjCZTNBytMwrUuiAnherNUZktlhPTKoF/sEk=
+github.com/dave/jennifer v1.3.0/go.mod h1:fIb+770HOpJ2fmN9EPPKOqm1vMGhB+TwXKMZhrIygKg=
+github.com/go-fed/activity v0.4.0 h1:1YOYLMT+x2hx+AtQZNQHOGBXWnn2CF/10jGxTjaOEsw=
+github.com/go-fed/activity v0.4.0/go.mod h1:QeFu271luhA2o47U3/DR6iWtxiB9Fw2dKGbvL8edM9E=
+github.com/go-fed/httpsig v0.1.0 h1:6F2OxRVnNTN4OPN+Mc2jxs2WEay9/qiHT/jphlvAwIY=
 github.com/go-fed/httpsig v0.1.0/go.mod h1:T56HUNYZUQ1AGUzhAYPugZfp36sKApVnGBgKlIY+aIE=
 github.com/go-test/deep v1.0.1 h1:UQhStjbkDClarlmv0am7OXXO4/GaPdCGiUiMTvi28sg=
 github.com/go-test/deep v1.0.1/go.mod h1:wGDj63lr65AM2AQyKZd/NYHGb0R+1RLqB8NKt3aSFNA=
+github.com/golang/mock v1.2.0 h1:28o5sBqPkBsMGnC6b4MvE2TzSr5/AT4c/1fLqVGIwlk=
+github.com/golang/mock v1.2.0/go.mod h1:oTYuIxOrZwtPieC+H1uAHpcLFnEyAGVDL/k47Jfbm0A=
 golang.org/x/crypto v0.0.0-20180527072434-ab813273cd59 h1:hk3yo72LXLapY9EXVttc3Z1rLOxT9IuAPPX3GpY2+jo=
 golang.org/x/crypto v0.0.0-20180527072434-ab813273cd59/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
 golang.org/x/sys v0.0.0-20180525142821-c11f84a56e43 h1:PvnWIWTbA7gsEBkKjt0HV9hckYfcqYv8s/ju7ArZ0do=
 golang.org/x/sys v0.0.0-20180525142821-c11f84a56e43/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
-golang.org/x/time v0.0.0-20180412165947-fbb02b2291d2 h1:+DCIGbF/swA92ohVg0//6X2IVY3KZs6p9mix0ziNYJM=
 golang.org/x/time v0.0.0-20180412165947-fbb02b2291d2/go.mod h1:tRJNPiyCQ0inRvYxbN9jk5I+vvW/OXSQhTDSoE431IQ=