upgrade to Kotlin 1.4.20

[oshai]

upgrade to Kotlin 1.3.61 -> 1.4.20
upgrade coroutines 1.3.2 -> 1.4.2
upgrade gradle 6.4.1 -> 6.7.1

[codecov]

Codecov Report

Merging #216 (6ed1a30) into master (0812e5e) will decrease coverage by 0.39%.
The diff coverage is 57.14%.

@@             Coverage Diff              @@
##             master     #216      +/-   ##
============================================
- Coverage     80.27%   79.87%   -0.40%     
  Complexity     1032     1032              
============================================
  Files           259      259              
  Lines          3792     3802      +10     
  Branches        474      491      +17     
============================================
- Hits           3044     3037       -7     
- Misses          531      532       +1     
- Partials        217      233      +16     

Impacted Files	Coverage Δ	Complexity Δ
...ql/db/postgresql/encoders/StartupMessageEncoder.kt	83.33% <50.00%> (-16.67%)	2.00 <1.00> (ø)
.../db/postgresql/messages/frontend/StartupMessage.kt	100.00% <100.00%> (ø)	1.00 <1.00> (ø)
...gresql/encoders/ExecutePreparedStatementEncoder.kt	75.00% <0.00%> (-25.00%)	1.00% <0.00%> (ø%)
...ql/db/postgresql/encoders/CloseStatementEncoder.kt	66.66% <0.00%> (-16.67%)	2.00% <0.00%> (ø%)
...jasync/sql/db/mysql/encoder/QueryMessageEncoder.kt	85.71% <0.00%> (-14.29%)	2.00% <0.00%> (ø%)
...b/mysql/encoder/PreparedStatementPrepareEncoder.kt	85.71% <0.00%> (-14.29%)	2.00% <0.00%> (ø%)
...sql/db/postgresql/parsers/CommandCompleteParser.kt	90.00% <0.00%> (-10.00%)	3.00% <0.00%> (ø%)
...async/sql/db/postgresql/PreparedStatementHolder.kt	91.30% <0.00%> (-8.70%)	5.00% <0.00%> (ø%)
...gresql/encoders/PreparedStatementOpeningEncoder.kt	86.95% <0.00%> (-8.70%)	2.00% <0.00%> (ø%)
...a/com/github/jasync/sql/db/SuspendingConnection.kt	32.14% <0.00%> (-7.15%)	0.00% <0.00%> (ø%)
... and 11 more

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