Update readme.md (#129)

Author: sappharx

readme.md

@@ -272,7 +272,7 @@ const predicate = (a) => a > 2
 
 ## Contracts
 
-A contract specifies the obligations and guarentees of the behavior from a function or expression at runtime. This acts as a set of rules that are expected from the input and output of a function or expression, and errors are generally reported whenever a contract is violated.
+A contract specifies the obligations and guarantees of the behavior from a function or expression at runtime. This acts as a set of rules that are expected from the input and output of a function or expression, and errors are generally reported whenever a contract is violated.
 
 ```js
 // Define our contract : int -> int