Some typo's corrected (cartogram_animation.rst)

[DiGro]

source/docs/3/cartogram_animation.rst:111 Toolbox. double ==>> Double

source/docs/3/cartogram_animation.rst:136 value. Click ==>> value. Click m (removed space)

source/docs/3/cartogram_animation.rst:157 be a a reference ==>> removed one "a"

source/docs/3/cartogram_animation.rst:243 21 .The default ==>> 21. The default

source/docs/3/cartogram_animation.rst:285 25 . Back ==>> 25. Back