preprocessor: do not copy .go files from content tree

We still have not worked out a good strategy for when to (not) copy
files from a page root in the content tree to hugo/content. So for now
we simply add .go files to the list of ignored files.

This should be a no-op on the output.

Preprocessor-No-Write-Cache: true
Signed-off-by: Paul Jolly <[email protected]>
Change-Id: I64a9f814b79b241fb3e8c7ec6624f6a7a40880ed
Dispatch-Trailer: {"type":"trybot","CL":1169679,"patchset":2,"ref":"refs/changes/79/1169679/2","targetBranch":"alpha"}

internal/cmd/preprocessor/cmd/page.go

@@ -150,7 +150,7 @@ func (p *page) process() error {
 		// TODO: come up with a better approach to skipping certain files.
 		// Should this perhaps be an include-based approach?
 		switch filepath.Ext(n) {
-		case ".cue", ".golden":
+		case ".cue", ".golden", ".go":
 			continue
 		}