Cache composer cache

Signed-off-by: Michal Čihař <michal@cihar.com>

Conflicts:
	.travis.yml

Conflicts:
	.travis.yml
Merge branch 'MAINT_4_2_13' into QA_4_2
Merge branch 'QA_4_2' into MAINT_4_3_0
Merge branch 'MAINT_4_3_0' into QA_4_3