pipenv version clash workaround

Should close issues #18 / #21 with the least
bad workaround. I consider it unlikely that
many people using black and flake8-black would
be using anything older than black 19.3b0 which
is now over a year old.

README.rst

@@ -150,6 +150,12 @@ Version History
 ======= ============ ===========================================================
 Version Release date   Changes
 ------- ------------ -----------------------------------------------------------
+v0.1.2  2020-05-18   - Minimum requirement on black 19.3b0 or later is now
+                       implicit. This is a workaround for `pipenv issue 3928
+                       <https://github.com/pypa/pipenv/issues/3928>`_. Upgrade
+                       black if running flake8 gives an error like this:
+                       ``Flake8 failed to load plugin "BLK" due to __call__()
+                       got an unexpected keyword argument 'target_versions'.``
 v0.1.1  2019-08-26   - Option to use a (global) black configuration file,
                        contribution from
                        `Tomasz Grining <https://github.com/098799>`_.

flake8_black.py

@@ -14,7 +14,7 @@
 from flake8 import LOG
 
 
-__version__ = "0.1.1"
+__version__ = "0.1.2"
 
 black_prefix = "BLK"
 

setup.py

@@ -41,6 +41,6 @@ def get_version(fname="flake8_black.py"):
     ],
     keywords="PEP8",
     py_modules=["flake8_black"],
-    install_requires=["flake8 >= 3.0.0", "black >= 19.3b0"],
+    install_requires=["flake8 >= 3.0.0", "black"],
     entry_points={"flake8.extension": ["BLK = flake8_black:BlackStyleChecker"]},
 )