Update bootstrap-rtl version to 3.1.2.

Downloaded from: https://github.com/ratnic/bootstrap-rtl/releases/download/v3.1.2/bootstrap-rtl-v3.1.2.zip

Homepage: https://github.com/ratnic/bootstrap-rtl
Popularity: Has 123 stars, around 900 daily visitors, and the most popular project in countries with right to left scripts e.g. Farsi, Arabic, and Hebrew; According to the BitDeli during three months that it was working.