Fix memcache install for php 5.5 builds in travis


Hi

As you can see here:
https://travis-ci.org/yiisoft/yii/jobs/4871285/#L179
Some test are skipped for php 5.5. Those are the one dependent on memcache.

In php 5.4. builds this is just ok:
https://travis-ci.org/yiisoft/yii/jobs/4871284/#L41

There was just small bug in installation of memcache:
https://github.com/arvenil/yii/commit/3c339515d5ccb565c9389e4802ffbe4716902d35#L0R9
(https://github.com/yiisoft/yii/commit/26786ccbd60e603c3fe114fecab3a12ea97bb1a3#L0R9)

I have also switched this script back to `#!/bin/sh` by removing one bashizm:
https://github.com/arvenil/yii/commit/367c6dce7a4367f6d13cc35095c31cf277334c9e#L0R3
(https://github.com/yiisoft/yii/commit/aea124110ebdc996203a904adc7a109b96d7653e#L0L1)

And also silenced output for installing memcache in php 5.5 builds as this was done for previous versions:
https://github.com/arvenil/yii/commit/9a216ae3bb3a29ebd28ce8299897c72e74a75473#L0R17
(https://github.com/yiisoft/yii/pull/931, https://github.com/yiisoft/yii/pull/927)

In short: Tests in php 5.5 builds which use memcache should work now :)