Allow newer LTS versions when parsing .nvmrc

[edhulbert]

In the function that parses an .nvmrc file with value of lts/* , the only LTS versions "allowed" are 16 and 18. The LTS versions up to 22 should be added.

Reference:

nodejs-buildpack/src/nodejs/supply/supply.go

Lines 85 to 88 in f1292f7

	var LTS = map[string]int{
	"gallium": 16,
	"hydrogen": 18,
	}