add: defaultBlock in Contract.call() method

[toknT]

Add a protected property $defaultBlock in Contract.__construct()

from the rpc document eth.call can send defaultBlock but I can't find out how to use contract's call in pending block with current code.

[codecov-io]

Codecov Report

Merging #155 into master will increase coverage by <.01%. The diff coverage is 100%.

@@             Coverage Diff              @@
##             master     #155      +/-   ##
============================================
+ Coverage     87.76%   87.77%   +<.01%     
  Complexity      717      717              
============================================
  Files            47       47              
  Lines          1569     1570       +1     
============================================
+ Hits           1377     1378       +1     
  Misses          192      192

Impacted Files	Coverage Δ	Complexity Δ
src/Contract.php	77.41% <100%> (+0.06%)	150 <28> (ø)	:arrow_down:

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[sc0Vu]

@toknT Thanks for your PR. It looks good.

But there is defaultBlock in these api (https://github.com/ethereum/wiki/wiki/JavaScript-API#web3ethdefaultblock):

• web3.eth.getBalance()
• web3.eth.getCode()
• web3.eth.getTransactionCount()
• web3.eth.getStorageAt()
• web3.eth.call()
• contract.myMethod.call()
• contract.myMethod.estimateGas()

IMHO we should add defaultBlock to Eth.php instead Contract.php.