Fix Lint/DeprecatedOpenSSLConstant auto-correction of OpenSSL::Cipher to use lower case

[bdewater]

Testing on some Linux-based CI systems revealed the upper case cipher name is not always accepted, but lower case always is. I didn't ran into this when developing #7950

Example output on a random VM:

user@app1:~$ cat /etc/issue
Ubuntu 16.04.3 LTS \n \l
user@app1:~$ ruby --version
ruby 2.3.1p112 (2016-04-26 revision 54768) [x86_64-linux]
user@app1:~$ irb
irb(main):001:0> require 'openssl'
=> true
irb(main):002:0> OpenSSL::Cipher.new('AES-256-GCM')
RuntimeError: unsupported cipher algorithm (AES-256-GCM)
	from (irb):2:in `initialize'
	from (irb):2:in `new'
	from (irb):2
	from /home/deploy/.rbenv/versions/2.3.1/bin/irb:11:in `<main>'
irb(main):003:0> OpenSSL::Cipher.new('aes-256-gcm')
=> #<OpenSSL::Cipher:0x00560ce9b75470>

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[koic]

Good catch! Thank you!