[nautilus-actions] docs/reference/Makefile.am: fix version.dir.xml generation

[Pierre Wieser <pwieser src gnome org>]

commit bab36724775356a0ea10a89fe82e6b8da40e02bc
Author: Pierre Wieser <pwieser trychlos org>
Date:   Tue Feb 21 17:31:01 2017 +0100

    docs/reference/Makefile.am: fix version.dir.xml generation

 docs/reference/Makefile.am |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)
---
diff --git a/docs/reference/Makefile.am b/docs/reference/Makefile.am
index d60f29a..b9180ec 100644
--- a/docs/reference/Makefile.am
+++ b/docs/reference/Makefile.am
@@ -166,8 +166,7 @@ xml_in_files = \
 xml_files = $(xml_in_files:.xml.in=.xml)
 
 version_dir.xml: version.xml
-       rm -f $@
-       cat $< | $(SED) 's?^\([[:alnum:]]\.[[:alnum:]]\).*?\1?' > $@
+       if test ! -f $@; then cat $< | $(SED) 's?^\([[:alnum:]]\.[[:alnum:]]\).*?\1?' > $@; fi
 
 install-data-local: install-data-local-hook