Bump versions to release v2.0.0

[jonasbb]

bors r+

[codecov]

Codecov Report

Merging #491 (427b025) into master (8ad35a0) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #491   +/-   ##
=======================================
  Coverage   70.76%   70.76%           
=======================================
  Files          52       52           
  Lines        3599     3599           
=======================================
  Hits         2547     2547           
  Misses       1052     1052           

Impacted Files	Coverage Δ
serde_with/src/lib.rs	100.00% <ø> (ø)
serde_with_macros/src/lib.rs	0.00% <ø> (ø)

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[bors]

Build succeeded:

• Rustsec Audit
• Tests result