Remove undefined export of lexeme symbol

Replaced with `convert(String, ::Lexeme)`

src/Lexers.jl

@@ -5,7 +5,7 @@ export Token, pattern, Newline, Whitespace, Tab, Keyword, Quote, Natural, Identi
 export Glyph, Dot, Comma, Colon, Semicolon, ParenthesisLeft, ParenthesisRight, BracketLeft, BracketRight, BraceLeft, BraceRight, Plus, Minus, Asterisk, Slash, GreaterThan, LessThan, Equal, At, Exclamation, Question
 
 include("Lexeme.jl")
-export Lexeme, lexeme, token
+export Lexeme, token
 
 include("Lexer.jl")
 export Lexer, tokenize