When a decorator changes the return type of a function, that change is not detected.

Steps to reproduce

from typing import Callable
from functools import wraps

def cast_to_str(func) -> Callable[..., str]:
    @wraps(func)
    def wrapper(*args, **kwargs):
        return str(func(*args, **kwargs))
    return wrapper

@cast_to_str
def get_num() -> int:
    return 5

get_num().strip()
# [no-member] Instance of 'int' has no 'strip' member 

Current behavior

Return type of decorated function is set by the function declaration

Expected behavior

Return type of the function set by decorator

pylint --version output

pylint 2.1.1
astroid 2.0.4
Python 3.6.5 (default, May 14 2018, 11:01:09)
[GCC 4.2.1 Compatible Apple LLVM 9.1.0 (clang-902.0.39.1)]