Feat/change default gas price

[aarmoa]

• Changed default gas price from 500000000 to 160000000. The change is done on top of dev because master doesn't include the refactoring that moved the default gas price to the constants module

[codecov[bot]]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (b0ffc20) 71.91% compared to head (49cd55c) 72.00%. Report is 2 commits behind head on dev.

Files	Patch %	Lines
pyinjective/async_client.py	66.66%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #280 +/- ## ========================================== + Coverage 71.91% 72.00% +0.08% ========================================== Files 46 46 Lines 3141 3151 +10 Branches 284 284 ========================================== + Hits 2259 2269 +10 Misses 814 814 Partials 68 68 ```

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