configure: Use . file rather than source file.

source is a bash concept, so when /bin/sh points to another shell the
existing construct won't work.

Reference: https://bugs.gentoo.org/927055
Signed-off-by: Jaco Kroon <jaco@uls.co.za>

configure

@@ -15854,7 +15854,7 @@ else
 	PBX_JANSSON=1
 fi
 
-source ./third-party/versions.mak
+. ./third-party/versions.mak
 # Find required JWT support if bundled is not enabled.
 if test "$LIBJWT_BUNDLED" = "no" ; then
 

configure.ac

@@ -748,7 +748,7 @@ else
 	PBX_JANSSON=1
 fi
 
-source ./third-party/versions.mak
+. ./third-party/versions.mak
 # Find required JWT support if bundled is not enabled.
 if test "$LIBJWT_BUNDLED" = "no" ; then
 	AST_PKG_CONFIG_CHECK([LIBJWT], [libjwt >= $LIBJWT_VERSION])