Fix typo folowing

Author: philderbeast

cabal-testsuite/cabal.project

@@ -1,6 +1,6 @@
 -- This intercepting project is here to avoid tests picking up a cabal.project
 -- from a parent directory, such as the one in the root of the `haskell/cabal`
--- project itself. Having `optional-packages: .` avoids the folowing warning
+-- project itself. Having `optional-packages: .` avoids the following warning
 -- being added to the `.out` file:
 --   Warning: There are no packages or optional-packages in the project
 optional-packages: .