fix: typo in unknown segments

Rearrange regexps so "special" regexp catches everything not caught by other regexps.
Eliminates the "unknown" segment I added in #148.

In practice, the only time we would hit the "unknown" segment is for a few weird
characters that weren't already caught by the "special" segment, for example, the
? and unclosed ` in "a `?> b".  I figured that in those rare cases, we might as
well just call those characters "special".

Fixes #178, refs #148.

lib/index.js

@@ -33,18 +33,15 @@ const highlighters = [
 
   /(?<bracket>[()])/,
 
-  // Arithmetic, bitwise, comparison, and compound operators as listed in
-  // https://www.w3schools.com/sql/sql_operators.asp, https://www.tutorialspoint.com/sql/sql-operators.htm,
-  // https://data-flair.training/blogs/sql-operators/.
-  // Plus a few other symbols used in SQL statements: ,;:.
-  // Operators are arranged so that multi-character operators (ex: ">=") are parsed as one operator rather than two.
-  /(?<special>\^-=|\|\*=|\+=|-=|\*=|\/=|%=|&=|>=|<=|<>|!=|!<|!>|>>|<<|[+\-*/%&|^=><]|[,;:.])/,
-
   /(?<identifier>\b\w+\b|`(?:[^`\\]|\\.)*`)/,
 
   /(?<whitespace>\s+)/,
 
-  /(?<unknown>\.+?)/
+  // Multi-character arithmetic, bitwise, comparison, and compound operators as listed in
+  // https://www.w3schools.com/sql/sql_operators.asp, https://www.tutorialspoint.com/sql/sql-operators.htm,
+  // https://data-flair.training/blogs/sql-operators/, plus any single character (in particular ,:;.) not matched by
+  // the above regexps.
+  /(?<special>\^-=|\|\*=|\+=|-=|\*=|\/=|%=|&=|>=|<=|<>|!=|!<|!>|>>|<<|.)/
 ]
 
 // Regex of the shape /(?<token1>...)|(?<token2>...)|.../g