X fix test.go for mod build

go.mod is inside wcfs/ and if `go test ./...` is ran outside of it, it
autodetects to use GOPATH mode and fails to find imports used by wcfs.

Makefile

@@ -183,7 +183,7 @@ test.py.drd: bigfile/_bigfile.so wcfs/wcfs
 
 # run go tests
 test.go	:
-	$(GO) test -count=1 ./... # -count=1 disables tests caching
+	cd wcfs && $(GO) test -count=1 ./... # -count=1 disables tests caching
 
 
 # test pagefault for double/real faults - it should crash