Fix project version number.
https://github.com/sparsehash/sparsehash/issues/146
--- configure.ac.orig	2015-10-12 16:13:52.000000000 -0500
+++ configure.ac	2018-02-01 13:10:51.000000000 -0600
@@ -4,7 +4,7 @@
 # make sure we're interpreted by some minimal autoconf
 AC_PREREQ(2.57)
 
-AC_INIT(sparsehash, 2.0.2, google-sparsehash@googlegroups.com)
+AC_INIT(sparsehash, @VERSION@, google-sparsehash@googlegroups.com)
 # The argument here is just something that should be in the current directory
 # (for sanity checking)
 AC_CONFIG_SRCDIR(README)