literals.rdoc: Update for symbol literals

* doc/syntax/literals.rdoc (Symbols): now Symbols created by
  interpolation can be garbage collected.  patch by Yihang Ho in
  [ruby-core:67194].  [Bug #10671]
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git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49056 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
literals.rdoc: quoted symbol keys

* doc/syntax/literals.rdoc (Hashes): describe about quoted symbol
  keys.

[ci skip]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49057 b2dd03c8-39d4-4d8f-98ff-823fe69b080e