chore(version): update dev version to 3.4.2.dev0

[wpbonelli]

The existing development version string 3.dev4 is ordinally incorrect, use 3.4.2.dev0 as suggested here

[codecov]

Codecov Report

Merging #1861 (dc6a459) into develop (a644b52) will decrease coverage by 0.1%.
The diff coverage is 100.0%.

@@            Coverage Diff            @@
##           develop   #1861     +/-   ##
=========================================
- Coverage     72.3%   72.2%   -0.1%     
=========================================
  Files          256     256             
  Lines        56112   56112             
=========================================
- Hits         40575   40564     -11     
- Misses       15537   15548     +11     

Impacted Files	Coverage Δ
flopy/version.py	100.0% <100.0%> (ø)

... and 2 files with indirect coverage changes