Fix display array containing e or f

[bowenszhu]

With this PR, arrays that includes e or f are displayed correctly.

julia> using Symbolics

julia> r = @variables a b c d e f g h i j
10-element Vector{Num}:
 a
 b
 c
 d
 e
 f
 g
 h
 i
 j

julia> m = [a b c d
            b e f g
            c f h i
            d g i j]
4×4 Matrix{Num}:
 a  b  c  d
 b  e  f  g
 c  f  h  i
 d  g  i  j

julia> m *= [1, 2, 3, 4]
4-element Vector{Num}:
 a + 2b + 3c + 4d
 b + 2e + 3f + 4g
 c + 2f + 3h + 4i
 d + 2g + 3i + 4j

[ChrisRackauckas]

Weird issue 😅