Unpin Pipfile dependencies

See also: tmux-python/tmuxp@2e01c32

Author: tony

Pipfile

@@ -4,12 +4,12 @@ verify_ssl = true
 name = "pypi"
 
 [dev-packages]
-docutils = "==0.14"
-alagitpull = ">=0.0.22"
-Sphinx = ">=2.0.1"
-isort = "==4.3.18"
-flake8 = "==3.7.7"
-pytest = "==4.5.0"
+docutils = "*"
+alagitpull = "*"
+Sphinx = ">=2.0.0"
+isort = "*"
+flake8 = "*"
+pytest = "*"
 libtmux = {path = ".",editable = true}
 
 [packages]