Support reading compressed geojson

[halfabrane]

@Perados can you check if this fixes #199 ?

Usage:

spark.read.format("magellan")
  .option("type", "geojson")
  .load("$path_to_geojson.gz")

[codecov-io]

Codecov Report

Merging #200 into master will increase coverage by 0.05%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #200      +/-   ##
=========================================
+ Coverage   89.74%   89.8%   +0.05%     
=========================================
  Files          50      50              
  Lines        1745    1755      +10     
  Branches      117     128      +11     
=========================================
+ Hits         1566    1576      +10     
  Misses        179     179

Impacted Files	Coverage Δ
...ain/scala/magellan/mapreduce/WholeFileReader.scala	97.05% <100%> (+0.9%)	⬆️
src/main/scala/magellan/GeoJSONRelation.scala	100% <100%> (ø)	⬆️

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[Perados]

@harsha2010 It works, thank you! 🚀