v1.2.2

## Arrow v1.2.2

[Diff since v1.2.1](https://github.com/JuliaData/Arrow.jl/compare/v1.2.1...v1.2.2)


**Closed issues:**
- Segmentation Fault with Threads.@spawn + Tables.partitioner + write with compression (#82)
- Types deserialize differently during session in which they were written (#88)
- Producing unsigned dict encoding indices; should be signed (#112)
- Unsigned integers as indices in DictEncoded type (#113)
- DictEncoded doesn't write as DictEncoded (#116)
- Errors writing file with missing in categorical (#117)

**Merged pull requests:**
- Make compressed writing threadsafe (#118) (@quinnj)
- Rework dict encoding of PooledArray/CategoricalArray to fix outstandi… (#119) (@quinnj)