[tracker] g-ir-merge: Use env to locate python3

[Carlos Garnacho <carlosg src gnome org>]

commit 4187ceb8029193120f670bd1559448b70e17a823
Author: Carlos Garnacho <carlosg gnome org>
Date:   Thu Aug 3 20:48:10 2017 +0200

    g-ir-merge: Use env to locate python3
    
    Pointed out to fix build on FreeBSD, since python is not
    in /usr/bin.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=782091

 utils/g-ir-merge/g-ir-merge |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/utils/g-ir-merge/g-ir-merge b/utils/g-ir-merge/g-ir-merge
index 45ed5f5..e9bb19a 100755
--- a/utils/g-ir-merge/g-ir-merge
+++ b/utils/g-ir-merge/g-ir-merge
@@ -1,4 +1,4 @@
-#!/usr/bin/python3
+#!/usr/bin/env python3
 #
 # Copyright 2017, Sam Thursfield <sam afuera me uk>
 #