fix the copyright statement in configure.ac

configure.ac

 AC_PREREQ(2.59)
-AC_COPYRIGHT([Copyright (c) 2011-2015 Varnish Software AS])
+AC_COPYRIGHT([Copyright (c) 2015 UPLEX Nils Goroll Systemoptimierung])
 AC_INIT([libvmod-backend_dyn], [trunk])
 AC_CONFIG_MACRO_DIR([m4])
 m4_ifndef([VARNISH_VMOD_INCLUDES], AC_MSG_ERROR([Need varnish.m4 -- see README.rst]))