Add newest Sprig library so we get b32enc/b32dec

[technosophos]

I know that @rimusz would like a base32 encoder call in templates. If we pull the latest Sprig, we'll get that. Then we can generate btsync secrets with {{randAscii 32 | b32enc}}

[mboersma]

This was accomplished in #440 (if not well before that).