let(): bugfix: multiple expressions: wrong evaluation order
let(): bugfix: multiple expressions: wrong evaluation order

bin/modernish:
- On shells without a 'let' builtin, the let() optimisation
  introduced in 0b2495f introduced a bug: when multiple expressions
  are given per let() invocation, the trick with the preceding
  assignment caused the expressions to be evaluated in the wrong
  order. So go back to using ':' to abandon the result value of all
  expressions except the final.

modernish/modernish