Fix typo

Change-Id: I6c6246d14e11507e2b24a91304a2fef7ac3b9e22
Reviewed-on: https://gerrit.libreoffice.org/72965Reviewed-by: Julien Nabet <serval2412@yahoo.fr>
Tested-by: Julien Nabet <serval2412@yahoo.fr>

external/libexttextcat/README

 N-Gram-Based Text Categorization library
 
 This guesses the language that input text is written in. Fundamentally
-an adaption of wiseguys libtextcat extended to be UTF-8 aware.
+an adaptation of wiseguys libtextcat extended to be UTF-8 aware.
 
 It is hosted at: [https://wiki.documentfoundation.org/Libexttextcat]