[gtk-doc] configure: Fix tiny non POSIX complaint test usage

[Stefan Kost <stefkost src gnome org>]

commit 10b7725c98233ed61004a2bf145d0776a738bf92
Author: Naohiro Aota <naota gentoo org>
Date:   Wed Mar 5 00:37:35 2014 +0900

    configure: Fix tiny non POSIX complaint test usage
    
    https://bugzilla.gnome.org/show_bug.cgi?id=725663

 configure.ac |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 68dc0a6..c5b90c9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -214,7 +214,7 @@ dnl this is mostly to detect the date command on macosx that is quite cripled
 dnl  and broken too
 AC_MSG_CHECKING(whether date can output nanoseconds)
 date +%s.%N | grep -q 'N'
-if test "$?" == "1"; then
+if test "$?" = "1"; then
   TS_FMT="+%s.%N"
   ELAPSED_FMT="+%H:%M:%S.%N"
   AC_MSG_RESULT(yes)
@@ -228,7 +228,7 @@ AC_SUBST(ELAPSED_FMT)
 
 AC_MSG_CHECKING(whether date can format dates)
 date >/dev/null 2>&1 --utc --date @1.1 $ELAPSED_FMT
-if test "$?" == "0"; then
+if test "$?" = "0"; then
   DATE_FMT_CMD="date --utc $ELAPSED_FMT --date @0"
   AC_MSG_RESULT(yes)
 else