Fix compress example

[Lyrkan]

The current compress function of the README doesn't always return the expected value:

• with the given example ([1, 1, 2, 3, 4, 4, 4]) it actually output [1,2,3,4], not [1,2,3] (which seems logical)
• with [1,1,2,3,4] the last element is missing ([1,2,3])
• with a single-element or an empty list it returns undefined

This PR changes it so:

• compress([1, 1, 2, 3, 4, 4, 4]) returns [1, 2, 3, 4]
• compress([1, 1, 2, 3, 4]) also returns [1, 2, 3, 4]
• compress([1, 1]) returns [1]
• compress([1]) returns [1]
• compress([]) returns []

[leonardiwagner]

thank you, sorry for the late approval