cmd/go/testdata/script/mod_test: add missing test invocation for case e

Change-Id: Ib0544adc1444a473f8edcb9dd92aefa9fcbc7330
Reviewed-on: https://go-review.googlesource.com/134656Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/go/testdata/script/mod_test.txt

 env GO111MODULE=on
 
+# TODO(bcmills): Convert the 'go test' calls below to 'go list -test' once 'go
+# list' is more sensitive to package loading errors.
+
 # A test in the module's root package should work.
 cd a/
 cp go.mod.empty go.mod
@@ -48,6 +51,10 @@ cd ../d_test
 go test
 stdout PASS
 
+cd ../e
+go test
+stdout PASS
+
 -- a/go.mod.empty --
 module example.com/user/a