Warnings compiling solidity contracts

[mfornet]

Compilation of solidity contracts emits several warnings. To see this locally use:

cd contracts/eth/nearbridge
./dist.sh

Warnings

• [x] truffle-flattener is using old version of solidity-parser. This warning is already solved: https://github.com/solidity-parser/parser/issues/19

 Warning: Accessing non-existent property 'INVALID_ALT_NUMBER' of module exports inside circular dependency

• [ ] No License on solidity code triggers warning. Consider using this approach (Only keep one License rather than removing all of them).

  dist/Borsh.full.sol: Warning: SPDX license identifier not provided in source file. Before publishing, consider adding a comment containing "SPDX-License-Identifier: <SPDX-License>" to each source file. Use "SPDX-License-Identifier: UNLICENSED" for non-open-source code. Please see https://spdx.org for more information.

• [x] Some docstring will stop working on version 0.7.0 of solidity

  dist/NearBridge.full.sol:529:17: Warning: Only state variables can have a docstring. This will be disallowed in 0.7.0.
      bytes32 epoch_id;           /// Epoch start hash of this block's epoch. Used for retrieving validator information
              ^------^

• [x] Warning: Function state mutability can be restricted to pure

dist/NearDecoder.full.sol:464:5: Warning: Function state mutability can be restricted to pure
    function decodeInitialValidators(Borsh.Data memory data) internal view returns(InitialValidators memory validators) {
    ^ (Relevant source part starts here and spans across multiple lines).

• [ ] Installing gyp/scrypt view log

[KaiserKarel]

I can check this out this weekend.

[mfornet]

Some warnings solved on #553