geography/geos: Update to 3.7.1.

upstream changelog:

Changes in 3.7.1
2018-11-29

- Bug fixes / improvements
  - Fix crash in GEOSCoordSeq_isCCW with empty coordseq
    (#927, Sergey Fedoseev)
  - Fix crash in GEOSInterpolate with empty LineString
    (#926, Sergey Fedoseev)
  - Fix crash in GEOSUnaryUnion with empty LineString
    (#928, Sergey Fedoseev)
  - Fix memory leak in SIRtree::insert (#919, Dan Baston)
  - Reduce required autoconf to 2.63
    (#56, John Harvey)
  - Fix incorrect return values on error from GEOSLength
    GEOSisValidDetail (#941, Dan Baston)

(gdt)