Fix rendering of templates in v6 and SF >= 3.2

[gregurco]

Q	A
Bug fix	yes
New feature	no
BC breaks	no
Deprecations	no
Tests pass	yes
Fixed tickets	#199
License	MIT

The staff related to calling of templates really was changed in SF3.2. I did changes and I guess we have next cases:

• PHP 5, SF 3.1 -> Guzzle Bundle v6.2.0
• PHP 5, SF 3.2 -> Guzzle Bundle v6.2.1 (new release with this fix)
• PHP 7, SF 3.2 -> Guzzle Bundle v7