Windows: Use the Windows style PATH separator ';'.

Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>
diff --git a/exec_cmd.c b/exec_cmd.c
index e189cac..a1bc4e0 100644
--- a/exec_cmd.c
+++ b/exec_cmd.c
@@ -37,7 +37,7 @@
 		else
 			strbuf_addstr(out, make_absolute_path(path));
 
-		strbuf_addch(out, ':');
+		strbuf_addch(out, PATH_SEP);
 	}
 }