Bump version for release.

NEWS

@@ -1,4 +1,4 @@
-1.6.3.dev0
+1.6.3
  * #541: Add "borgmatic list --find" flag for searching for files across multiple archives, useful
    for hunting down that file you accidentally deleted so you can extract it. See the documentation
    for more information:

setup.py

@@ -1,6 +1,6 @@
 from setuptools import find_packages, setup
 
-VERSION = '1.6.3.dev0'
+VERSION = '1.6.3'
 
 
 setup(