17.4.0.dev0 bump (#694)

diff --git a/src/OpenSSL/version.py b/src/OpenSSL/version.py
index 274d24c..9a2f9d8 100644
--- a/src/OpenSSL/version.py
+++ b/src/OpenSSL/version.py
@@ -11,7 +11,7 @@
     "__title__", "__uri__", "__version__",
 ]
 
-__version__ = "17.3.0"
+__version__ = "17.4.0.dev0"
 
 __title__ = "pyOpenSSL"
 __uri__ = "https://pyopenssl.org/"