main: 'type' keyword should always be evaluated

Resolves #21. When using `-k` option, gomtree should use
only the keywords specified by the user, as well as the 'type'
keyword if it wasn't specified.

Signed-off-by: Stephen Chung <schung@redhat.com>

cmd/gomtree/main.go

@@ -47,6 +47,9 @@ func main() {
 	// -k <keywords>
 	if *flUseKeywords != "" {
 		currentKeywords = splitKeywordsArg(*flUseKeywords)
+		if !inSlice("type", currentKeywords) {
+			currentKeywords = append([]string{"type"}, currentKeywords...)
+		}
 	} else {
 		currentKeywords = mtree.DefaultKeywords[:]
 	}