PROTON-1926, PROTON-1944: restore versions for 0.26.0-rc2

This reverts commit 1b554aad70452d6501cb3e13a6c10186d14e9dc9.
diff --git a/VERSION.txt b/VERSION.txt
index 7e9b4cf..4e8f395 100644
--- a/VERSION.txt
+++ b/VERSION.txt
@@ -1 +1 @@
-0.27.0-SNAPSHOT
+0.26.0
diff --git a/python/docs/conf.py b/python/docs/conf.py
index 476cf29..59317d4 100644
--- a/python/docs/conf.py
+++ b/python/docs/conf.py
@@ -48,9 +48,9 @@
 # built documents.
 #
 # The short X.Y version.
-version = '0.27.0'
+version = '0.26.0'
 # The full version, including alpha/beta/rc tags.
-release = '0.27.0-SNAPSHOT'
+release = '0.26.0'
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.