[CSL-1014] Add '*.tix' (test coverage) files to '.gitignore'
[CSL-1014] Add '*.tix' (test coverage) files to '.gitignore'

input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype,input-output-hk/pos-haskell-prototype,input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype