correct type parameter seq in RWST

[kailuowang]

fixes #1763

[codecov-io]

Codecov Report

Merging #1765 into master will decrease coverage by <.01%.
The diff coverage is 94.11%.

@@            Coverage Diff             @@
##           master    #1765      +/-   ##
==========================================
- Coverage   94.17%   94.17%   -0.01%     
==========================================
  Files         256      256              
  Lines        4208     4206       -2     
  Branches       93       97       +4     
==========================================
- Hits         3963     3961       -2     
  Misses        245      245

Impacted Files	Coverage Δ
...rc/main/scala/cats/laws/discipline/Arbitrary.scala	92.06% <ø> (ø)	⬆️
.../src/main/scala/cats/data/ReaderWriterStateT.scala	95.78% <94.11%> (-0.09%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update cb84fd4...0481156. Read the comment docs.

[peterneyens]

Thanks for picking this up @kailuowang.