Use canonical form for true in yaml

[cmungall]

Always use canonical forms true and false for bools in YAML

This will ensure future proofing for yaml 1.2, frameworks like rueyaml, etc

The status of non-canonical forms in 1.2 is a little unclear

https://stackoverflow.com/questions/42283732/are-on-and-off-supposed-to-be-interpreted-as-true-or-false-in-yaml-1-2

[matentzn]

oooooh oh. Almost all odk config files in existence have upper casing. Well, better late than never..