Update pep-0515.rst

Support Unicode imaginary signs,

https://codepoints.net/U+2148, https://codepoints.net/U+2149

https://discourse.julialang.org/t/what-is-the-unicode-for-the-number-i-the-imaginary-unit-of-the-complex-numbers/30904

peps/pep-0515.rst

@@ -67,7 +67,7 @@ For floating-point and complex literals::
    digitpart: digit (["_"] digit)*
    fraction: "." digitpart
    exponent: ("e" | "E") ["+" | "-"] digitpart
-   imagnumber: (floatnumber | digitpart) ("j" | "J")
+   imagnumber: (floatnumber | digitpart) ("j" | "J" | "ⅈ" | "ⅉ" | "𝑖")
 
 Constructors
 ------------