docs: remove 3.4 from supported versions list (#549)

Remove 3.4 from the supported versions list. We no longer actively test it and it has been EOL since March. https://www.python.org/downloads/release/python-3410/
diff --git a/README.rst b/README.rst
index c9c411f..10de0ac 100644
--- a/README.rst
+++ b/README.rst
@@ -24,7 +24,7 @@
 
 Supported Python Versions
 ^^^^^^^^^^^^^^^^^^^^^^^^^
-Python >= 3.4
+Python >= 3.5
 
 Deprecated Python Versions
 ^^^^^^^^^^^^^^^^^^^^^^^^^^