rmapshaper 0.6.0

• Updated bundled mapshaper version to v0.6.113 (#179).
• Bumped minimum geojsonsf version to 2.0.5 to handle logical properties correctly (#177).
• v8_version() now works correctly in startup checks (#173, thanks @elipousson).
• Added a more proactive startup message regarding old v8 engines, as the new
  bundled mapshaper library will not work with libv8 < 8.1.307.30 (#140).
• Added pkgdown site at https://andyteucher.ca/rmapshaper/
• Setting force_FC = TRUE no longer adds a rmapshaperid id column. force_FC
  is also better respected across functions and methods; previously it was
  somewhat inconsistent (#151).
• Added new argument gj2008 to all functions, which if TRUE outputs geojson following the old
  (2008) specification. Polygon rings are CW and holes are CCW, which is the
  opposite of the default RFC 7946-compatible output. This is required by D3, and
  packages that depend on it, like plotly (#167, #168).