Disable failing doctest

This doctest annotates the output of `divisors(60)`, which is nice, but Documenter doesn't like it. So just turn it into a plain code block without any testing.

Author: fingolfin

src/Primes.jl

@@ -968,7 +968,7 @@ For convenience, `divisors(0)` returns `[]`.
 
 # Example
 
-```jldoctest
+```julia
 julia> divisors(60)
 12-element Vector{Int64}:
   1         # 1
@@ -983,7 +983,8 @@ julia> divisors(60)
  15         # 5 * 3
  30         # 5 * 3 * 2
  60         # 5 * 3 * 2 * 2
-
+```
+```jldoctest
 julia> divisors(-10)
 4-element Vector{Int64}:
   1