Fix typo on chapter 2: catagory -> category
Fix typos in Chapter 2

 * assesing -> assessing
 * Determinstic -> Deterministic
 * implicity -> implicitly
 * determinsitic -> deterministic
 * intial -> initial
 * probablistic -> probabilistic
 * amoung -> among
 * explict -> explicit
 * implicity -> implicitly
 * paramters -> parameters
 * Farhenhit -> Fahrenheit
 * ocuring -> occurring
 * probabilties -> probabilities
 * specificed -> specified
 * artifical -> artificial
Merge pull request #57 from pablooliveira/Chapter2-typo

Fix typos in Chapter 2