message: doc: fix typo: expresison -> expression
  PR
diff: @@ -72,7 +72,7 @@ impl LiteralSearcher {
  /// Returns true if all matches comprise the entire regular expression.
  ///
  /// This does not necessarily mean that a literal match implies a match
  - /// of the regular expression. For example, the regular expresison `^a`
  + /// of the regular expression. For example, the regular expression `^a`
  /// is comprised of a single complete literal `a`, but the regular
  /// expression demands that it only match at the beginning of a string.
  pub fn complete(&self) -> bool {
  