[FIXED #83837394] Removed deprecation warning during grunt build

- upgraded grunt-contrib-sass to 0.8.1 which fixes wrong command line arguments: *--sourcemap=auto* instead *--sourcemap auto*
- removed unnecessary sourcemap option - grunt-contrib-sass generates sourcesmaps by default
- removed "grunt-contrib-sass" from **devDependencies** - there is no need to place it there if it is already in **depedencies**