Fix travis build error, old apr tarball doesn't exist anymore
Fix travis build error, old apr tarball doesn't exist anymore

```
$ wget http://ftp.jaist.ac.jp/pub/apache/apr/${APR}.tar.gz
--2018-09-21 07:16:24--  http://ftp.jaist.ac.jp/pub/apache/apr/apr-1.6.3.tar.gz
Resolving ftp.jaist.ac.jp (ftp.jaist.ac.jp)... 150.65.7.130, 2001:df0:2ed:feed::feed
Connecting to ftp.jaist.ac.jp (ftp.jaist.ac.jp)|150.65.7.130|:80... connected.
HTTP request sent, awaiting response... 404 Not Found
2018-09-21 07:16:25 ERROR 404: Not Found.
```

ashwinstar/gpdb,lisakowen/gpdb,50wu/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,adam8157/gpdb,50wu/gpdb,xinzweb/gpdb,greenplum-db/gpdb,adam8157/gpdb,lisakowen/gpdb,jmcatamney/gpdb,50wu/gpdb,adam8157/gpdb,ashwinstar/gpdb,50wu/gpdb,adam8157/gpdb,adam8157/gpdb,xinzweb/gpdb,50wu/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,lisakowen/gpdb,ashwinstar/gpdb,50wu/gpdb,50wu/gpdb,lisakowen/gpdb,ashwinstar/gpdb,lisakowen/gpdb,xinzweb/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,adam8157/gpdb,lisakowen/gpdb,adam8157/gpdb,50wu/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,xinzweb/gpdb,greenplum-db/gpdb,xinzweb/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,xinzweb/gpdb,adam8157/gpdb,lisakowen/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,xinzweb/gpdb,xinzweb/gpdb,lisakowen/gpdb