fix line chart renderer crash: can't form range when end < start

[liuxuan30]

ChartsDemo will crash all the time for the Line Chart1 Chart view controller,
This PR fix the line chart renderer crash: can't form range when end < start while phaseX is 0 (from + 1 ..< from + 0 is crashing); use stride instead, seems stride can gracefully fail the loop

@danielgindi I clicked the charts demo one by one, seems others are good, but I'm not sure if any of the rest for loops will have similar issue. Let's fix what we met first.

[liuxuan30]

@petester42 I see builds keep failing for swift 3? How can we fix it, or we wait for Travis CI to fix? Seems the test machine's compiler is not 2.2 yet.

[pmairoldi]

Travis has to update for it to work.

[liuxuan30]

@petester42 what a quick reply! Thanks

[danielgindi]

Yeah I've just tried to update the travis configuration file, as they've added xcode 7.3 to their supported version. Let's see if it builds :-)

[liuxuan30]

reran today, still complier error :(
however the error log is not the same:

/Users/travis/build/danielgindi/ios-charts/Charts/Carthage/Checkouts/ios-snapshot-test-case/FBSnapshotTestCase/SwiftSupport.swift:63:30: 
error: cannot convert value of type 'String' to expected argument type 'StaticString'

A shell task failed with exit code 65:

** BUILD FAILED **

seems we have to update FBSnapshotTestCase?