internal/fetch: use a valid semantic version for local modules

Currently, local module processing fails due to having an invalid
semantic version, so use "v0.0.0" instead of "latest" as a default.

Change-Id: I7e7cbc1c6b2ef8dd0423233b575b46ab2a6a65a2
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/280620
Reviewed-by: Jonathan Amsterdam <jba@google.com>
Trust: Julie Qiu <julie@golang.org>
Run-TryBot: Julie Qiu <julie@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
diff --git a/internal/fetch/fetchlocal.go b/internal/fetch/fetchlocal.go
index 8f171b3..8c12ed2 100644
--- a/internal/fetch/fetchlocal.go
+++ b/internal/fetch/fetchlocal.go
@@ -25,7 +25,7 @@
 // Version and commit time are pre specified when fetching a local module, as these
 // fields are normally obtained from a proxy.
 var (
-	LocalVersion    = "latest"
+	LocalVersion    = "v0.0.0"
 	LocalCommitTime = time.Time{}
 )