Fix an incorrect auto-correct for Style/SingleLineMethods

[koic]

Fix the following incorrect auto-correct for Style/SingleLineMethods when using single line class method definition.

% cat example.rb
def self.some_method; body end

% rubocop --only Style/SingleLineMethods -a
(snip)

Offenses:

example.rb:1:1: C: [Corrected] Style/SingleLineMethods: Avoid
single-line method definitions.
def self.some_method; body end
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

1 file inspected, 1 offense detected, 1 offense corrected

Before

% cat example.rb
def some_method() = body

self is lost due to auto-correction.

After

% cat example.rb
def self.some_method() = body

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• Added tests.
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