Fix "text" ctype in smb_enumshares

"text" is not a valid ctype, should be text/plain.

- [ ] Use auxiliary/scanner/smb/smb_enumshares
- [ ] Have a valid username/pass
- [ ] Set ```SpiderShares``` to true
- [ ] Set ```ShowFiles``` to true
- [ ] Set ```LogSpider``` between 1, 2 or 3
- [ ] Run the module. It should list all the files found, and store the results with a store_loot as *.txt