Gaston v2.0.2

Diff since v2.0.1

Merged pull requests:

• fix ColorSchemes.resample requirement (#197) (@t-bltg)
• replace GASTON_VERSION with Base.pkgversion (#199) (@t-bltg)
• restore GNUPLOT_VERSION for Plots (#200) (@t-bltg)
• fix JULIA_GNUPLOT_EXE usage (#202) (@t-bltg)

Closed issues:

• Compilation error after upgrading to 2.0 (#196)
• CODECOV_TOKEN (#198)