Vararg closures don't round-trip properly through string conversion

[Keno]

Printing exprs drops parens around .... Usually this is fine, because the parens are non-significant,
but it matters in anonymous function syntax.

julia> Meta.parse(string(:((args...)->args)))
ERROR: Base.Meta.ParseError("extra token \"->\" after end of expression")
Stacktrace:
 [1] parse(::String, ::Int64; greedy::Bool, raise::Bool, depwarn::Bool) at ./meta.jl:186
 [2] parse(::String; raise::Bool, depwarn::Bool) at ./meta.jl:217
 [3] parse(::String) at ./meta.jl:217
 [4] top-level scope at REPL[1]:1

julia> (args...)->args
#1 (generic function with 1 method)