added a new SYMFONY_REQUIRE env

[prisis]

Q	A
Bug fix?	yes
New feature?	yes
BC breaks?	no
Deprecations?	no
Related tickets	#46
License	MIT
Doc PR	-

removed symfony packages version from source

[codecov]

Codecov Report

Merging #47 into master will increase coverage by 0.68%.
The diff coverage is 55.55%.

@@             Coverage Diff              @@
##             master      #47      +/-   ##
============================================
+ Coverage     51.94%   52.62%   +0.68%     
- Complexity      560      565       +5     
============================================
  Files            38       38              
  Lines          1490     1503      +13     
============================================
+ Hits            774      791      +17     
+ Misses          716      712       -4

Impacted Files	Coverage Δ	Complexity Δ
...tomatic/Prefetcher/TruncatedComposerRepository.php	72.72% <100%> (+22.72%)	4 <1> (+1)	⬆️
src/Automatic/Prefetcher/Cache.php	20.83% <31.25%> (+20.83%)	14 <2> (+2)	⬆️
src/Automatic/Automatic.php	34.76% <80%> (+0.76%)	112 <0> (+2)	⬆️
src/Automatic/Container.php	57.14% <0%> (+3.29%)	5% <0%> (ø)	⬇️

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