configure.ac: Ensure whitespace after each comma

For increased consistency and readability.

This restores the spaces removed on commit bf81cd6 ("configure.ac: run
autoupdate to fix autoconf warning") / PR #4316.

Command used to check for the lack of whitespace:

    grep ',[^ ]' configure.ac

configure.ac

@@ -12,9 +12,10 @@
 #
 
 AC_PREREQ([2.68])
-AC_INIT([firejail],[0.9.67],[[email protected]],[],[https://firejail.wordpress.com])
-AC_CONFIG_SRCDIR([src/firejail/main.c])
+AC_INIT([firejail], [0.9.67], [[email protected]], [],
+ [https://firejail.wordpress.com])
 
+AC_CONFIG_SRCDIR([src/firejail/main.c])
 AC_CONFIG_MACRO_DIR([m4])
 
 AC_PROG_CC