fix double-space

Author: RalfJung

src/tokens.md

@@ -151,7 +151,7 @@ A _string literal_ is a sequence of any Unicode characters enclosed within two
 which must be _escaped_ by a preceding `U+005C` character (`\`).
 
 Line-breaks are allowed in string literals. A line-break is either a newline
-(`U+000A`) or a pair of carriage return and  newline (`U+000D`, `U+000A`). Both
+(`U+000A`) or a pair of carriage return and newline (`U+000D`, `U+000A`). Both
 byte sequences are normally translated to `U+000A`, but as a special exception,
 when an unescaped `U+005C` character (`\`) occurs immediately before the
 line-break, the `U+005C` character, the line-break, and all whitespace at the