update README.rst to reflect dropping Python 2.7
diff --git a/README.rst b/README.rst
index e13497e..f1c9c5d 100644
--- a/README.rst
+++ b/README.rst
@@ -15,7 +15,7 @@
 Dependencies
 ============
 
-- CPython_ 2.7+ or 3.4+, pypy_ 2.0+. Older versions may work, but are not
+- CPython_ 3.4+, pypy_ 2.0+. Older versions may work, but are not
   recommended as there is no automated regression testing set up for them.
 - libusb-1.0_