Write a RandomCipher function that builds a dictionary where each of the 26 letters of the alphabet is randomly matched to another (all lowercase). Each of the matching letters should be unique (in other words, your function creates a bijective mapping). Example:

{ 'a':'g', 'b':'i', 'c':'b', 'd':'d', 'e':'y', 'f':'q', 'g':'a', 'h':'p', 'i':'i', 'j':'c', 'k':'y', 'l':'z', 'm':'w',

'n':'c', 'o':'v', 'p':'z', 'q':'s', 'r':'h', 's':'x', 't':'e', 'u':'v', 'v':'p', 'w':'s', 'x':'j', 'y':'f', 'z':'w' }