Update image to prevent GLIBC_2.29 not found error

[MrBlenny]

When running the existing dockerfile as described

$ docker build -t tippecanoe:latest .
$ docker run -it --rm \
  -v /tiledata:/data \
  tippecanoe:latest \
  tippecanoe --output=/data/output.mbtiles /data/example.geojson

The following errors is thrown

tippecanoe: /lib/x86_64-linux-gnu/libm.so.6: version `GLIBC_2.29' not found (required by tippecanoe)

This is resolved by updating the dockerfile's ubuntu version to one which has a newer GLIBC.