maven-helper: need to special-case get_mtime also on Windows

Chances are that developers try to use the shell scripts with the Git
Bash, but the Git for Windows installer does not install the stat(1)
utility. So fall back to using GNU date(1)'s -r option.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

bin/maven-helper.sh

@@ -18,12 +18,18 @@ die () {
 get_mtime () {
 	stat -c %Y "$1"
 }
-if test Darwin = "$(uname -s 2> /dev/null)"
-then
+case "$(uname -s 2> /dev/null)" in
+MINGW*)
+	get_mtime () {
+		date -r "$1" +%s
+	}
+	;;
+Darwin)
 	get_mtime () {
 		stat -f %m "$1"
 	}
-fi
+	;;
+esac
 
 # Parse <groupId>:<artifactId>:<version> triplets (i.e. GAV parameters)