update codecov-action to v2 and fix codecov flags

[zchee]

update codecov-action to v2 and fix codecov flags

[codecov]

Codecov Report

Merging #121 (c6fb690) into master (6afca42) will decrease coverage by 64.4%.
The diff coverage is n/a.

❗ Current head c6fb690 differs from pull request most recent head 9892133. Consider uploading reports for the commit 9892133 to get more accurate results

@@           Coverage Diff            @@
##           master   #121      +/-   ##
========================================
- Coverage    64.4%      0   -64.5%     
========================================
  Files          14      0      -14     
  Lines        2114      0    -2114     
========================================
- Hits         1362      0    -1362     
+ Misses        615      0     -615     
+ Partials      137      0     -137     

Flag	Coverage Δ
linux-1.15	?
linux-1.16	?
linux-1.17	?
macos-1.15	?
macos-1.16	?
macos-1.17	?
windows-1.15	?
windows-1.16	?
windows-1.17	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
msgpack/unpack.go
nvim/api.go
nvim/plugin/main.go
msgpack/pack.go
nvim/types.go
msgpack/encode.go
msgpack/msgpack.go
nvim/plugin/plugin.go
msgpack/rpc/rpc.go
msgpack/field.go
... and 4 more

---

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 6afca42...9892133. Read the comment docs.