cmd/gopherbot: match just the whole word document

When the title contains the word document then
repeat the check with a regex word boundaries rule then
return positive just in case of a whole word match.

Updates golang/go#31153

cmd/gopherbot/gopherbot.go

@@ -19,6 +19,7 @@ import (
 	"net/http"
 	"os"
 	"path/filepath"
+	"regexp"
 	"sort"
 	"strconv"
 	"strings"
@@ -1988,8 +1989,11 @@ func isDocumentationTitle(t string) bool {
 	if strings.Contains(t, "godoc:") { // in x/tools, or the dozen places people file it as
 		return false
 	}
-	return strings.Contains(t, "documentation") ||
-		strings.Contains(t, "docs ")
+	if strings.Contains(t, "docs ") {
+		return true
+	}
+	return strings.Contains(t, "document") &&
+		regexp.MustCompile(`\bdocument\b`).MatchString(t)
 }
 
 func isGoplsTitle(t string) bool {