Fix 'pragma solidity' parsing

[gsalzer]

remove comments and strings before searching for a line containing 'pragma solidity'

[gsalzer]

The patch tries to be minimally invasive; you may want to integrate it better. The comment citing the source can be removed (no need to give credits), it is just to inspire trust (?) that the code works since we used it for processing source codes in one of our studies.

[norhh]

For some reason, I’ve lost access to the CircleCI pipeline results over the past month. @psantos-consensys, could you look into the cause of CircleCI’s failure? Additionally, could you change the permissions to view Mythril’s CircleCI results? Since Mythril is open-source, these results should ideally be public as they were previously.