wezterm.terminfo: add terminator to Sync capability

[gpanders]

I'm not sure if this is strictly necessary, but according to the
terminfo specification 1, a conditional string should be terminated
with %;.

Quoting the relevant section:

%? expr %t thenpart %e elsepart %;
     This forms an if-then-else.  The %e elsepart is optional.
     Usually the %? expr part pushes a value onto the stack, and
     %t pops it from the stack, testing if it is nonzero (true).
     If it is zero (false), control passes to the %e (else) part.

[wez]

Seems reasonable, thanks!