hazard/writers, risk/writers:

Loss Map and Hazard Map node values are written to json as floats,
not strings.
tests/hazard/writers_test, tests/risk/writers_test:

Updated tests to match geojson loss/hazard map output changes.
Merge pull request #107 from larsbutler/geojson-float-map-values

GeoJSON map node values should be floats

[r=matley] [f=1224399]