values coerced to numbers (floats) for stacking
Better test name
parseFloat -> +
Merge branch 'develop' into stackString

Conflicts:
	test/components/plots/stackedPlotTests.ts
	test/tests.js
Coerce to number
Account for stackedArea
Merge pull request #1185 from palantir/stackString

[StackedPlot] - Strings coerced to numbers for stacking