Hotfix: check for active transaction in commit and rollback methods

[roxblnfk]

Alternative for #62

[codecov]

Codecov Report

Merging #66 (567cbe4) into master (4818807) will decrease coverage by 0.43%.
The diff coverage is 23.07%.

@@             Coverage Diff              @@
##             master      #66      +/-   ##
============================================
- Coverage     92.90%   92.46%   -0.44%     
- Complexity     1476     1481       +5     
============================================
  Files            67       67              
  Lines          3804     3823      +19     
============================================
+ Hits           3534     3535       +1     
- Misses          270      288      +18     

Impacted Files	Coverage Δ	Complexity Δ
src/Driver/Driver.php	76.44% <21.73%> (-6.17%)	91.00 <0.00> (+5.00)	⬇️
src/Driver/Postgres/PostgresDriver.php	81.25% <33.33%> (-1.29%)	25.00 <0.00> (ø)

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