Cannot assign real numbers to Real

[DMR-coding]

• Are you reporting a bug, or opening a feature request?
  Reporting a bug

• Minimal repro:

from numbers import Real


def double(n: Real) -> float:
    return n * 2.0


print(double(1))
print(double(1.0))

• What is the actual behavior/output?

min_repro.py:8: error: Argument 1 to "double" has incompatible type "int"; expected "Real"
min_repro.py:9: error: Argument 1 to "double" has incompatible type "float"; expected "Real"

• What is the behavior/output you expect?
  No output-- isinstance(1, Real) and isinstance(1.0, Real) are both true.

• What are the versions of mypy and Python you are using?
  I am using 0.711. (I was not able to successfully install from master.)

• What are the mypy flags you are using? (For example --strict-optional)
  No flags

[ilevkivskyi]

Duplicate of #3186