[shopsys] composer.json: revert BC breaking change of snc/redis-bundle dependency

[PetrHeinz]

Q	A
Description, reason for the PR	In #978 the supported versions of snc/redis-bundle package were changed which breaks backward compatibility. Even though we don't define BC in terms of dependencies precisely (see #872), you cannot use shopsys/framework in version dev-master using the shopsys/project-base in the 7.0.0 version as a base repository without further changes (see below).
New feature	No
BC breaks	No
Fixes issues	...
Standards and tests pass	Yes
Have you read and signed our License Agreement for contributions?	Yes

When using shopsys/project-base in version 7.0.0 and replacing all shopsys/* dependencies to dev-master (current master is on b3128c4) version, following error is thrown during composer install:

Loading composer repositories with package information
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - shopsys/framework dev-master requires snc/redis-bundle ^2.1.7 -> satisfiable by snc/redis-bundle[2.1.8, 2.1.9].
    - snc/redis-bundle 2.1.8 conflicts with shopsys/framework[dev-master].
    - snc/redis-bundle 2.1.9 conflicts with shopsys/framework[dev-master].
    - Installation request for shopsys/framework dev-master -> satisfiable by shopsys/framework[dev-master].

The modification of composer.json was originally done in #978 so that Travis build succeeds (not sure about the exact reason). This goal of this PR is to pass on Travis while still being backward-compatible with shopsys/project-base in 7.0.0.

[boris-brtan]

maybe we could compare version of php extension for redis on travis and in our Dockerfile

RUN pecl install redis-4.1.1 && \
    docker-php-ext-enable redis

phpredis/phpredis/issues/1333
Kdyby/Redis#80
snc/SncRedisBundle#487 [2.1.8 lazyload for phpredis]

[PetrHeinz]

@boris-brtan You're right about the PECL extension version. There was 3.1.4 installed on Travis, we need 4.1.1. See https://travis-ci.org/shopsys/shopsys/builds/530758153 for details.

[boris-brtan]

HI,
thx for the fixes, i have just some questions and suggestions.
Maybe some additional information could be added into PR description.

[boris-brtan]

i just noticed another thing that in README.md there is not the same link for OK build to travis at it is for packages

[![Build Status](https://travis-ci.org/shopsys/migrations.svg?branch=master)](https://travis-ci.org/shopsys/migrations)

![travis-badge](https://travis-ci.org/shopsys/shopsys.svg?branch=master)

[PetrHeinz]

@boris-brtan Yes, there is a different alt text and it's not a link to the Travis page, but to the image itself. Could you create a PR to fix that please?