cmd/go: move mod_tidy.txt from testdata/mod to testdata/src

This file is clearly a script test, not a module definition, but it's in the
wrong directory to be run as one.

Fortunately, it passes with only minor modifications (changing “..” to “.”).

Change-Id: I66a544dfde82b8348108d2596c74e174157ae297
Reviewed-on: https://go-review.googlesource.com/127615
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/testdata/mod/mod_tidy.txt → src/cmd/go/testdata/script/mod_tidy.txt

@@ -19,11 +19,11 @@ require (
 	w.1 v1.2.0
 )
 
-replace x.1 v1.0.0 => ../x
-replace y.1 v1.0.0 => ../y
-replace z.1 v1.1.0 => ../z
-replace z.1 v1.2.0 => ../z
-replace w.1 => ../w
+replace x.1 v1.0.0 => ./x
+replace y.1 v1.0.0 => ./y
+replace z.1 v1.1.0 => ./z
+replace z.1 v1.2.0 => ./z
+replace w.1 => ./w
 
 -- m.go --
 package m