normalize input -same as goflags.NormalizedStringSliceOptions

[dogancanbakir]

$ cat domain.lst 
Google.com

$ go run . -dL domain.lst 

               __    _____           __         
   _______  __/ /_  / __(_)___  ____/ /__  _____
  / ___/ / / / __ \/ /_/ / __ \/ __  / _ \/ ___/
 (__  ) /_/ / /_/ / __/ / / / / /_/ /  __/ /    
/____/\__,_/_.___/_/ /_/_/ /_/\__,_/\___/_/

                projectdiscovery.io

[INF] Current subfinder version v2.6.4-dev (development)
[INF] Loading provider config from /home/vscode/.config/subfinder/provider-config.yaml
[INF] Enumerating subdomains for google.com

...
googleproxy-66-249-83-183.google.com
mailit0-f43.google.com
sandbox.r2.sn-n4v7snlr.c.pack.google.com
mailqk0-f152.google.com
alt83.www.google.com
alt2871.www.google.com
googleproxy-66-249-88-182.google.com
mail-ads.r4.sn-vgqsrnld.c.pack.google.com
[INF] Found 13386 subdomains for google.com in 20 seconds 394 milliseconds

Closes #1071.

[Mzack9999]

marking as Request Changes to review a minor suggested change