Downrade the version to 2.6.2-dev0 so we can install pylint easily

See #1077 (comment)

astroid/__pkginfo__.py

@@ -24,5 +24,5 @@
 # Licensed under the LGPL: https://www.gnu.org/licenses/old-licenses/lgpl-2.1.en.html
 # For details: https://github.com/PyCQA/astroid/blob/master/LICENSE
 
-__version__ = "2.7.0-dev0"
+__version__ = "2.6.2-dev0"
 version = __version__

doc/release.md

@@ -19,8 +19,8 @@ So, you want to release the `X.Y.Z` version of astroid ?
 Move back to a dev version with `tbump`:
 
 ```bash
-tbump X.Y+1.Z-dev0 --no-tag --no-push # You can interrupt during copyrite
-git commit -am "Upgrade the version to x.y+1.z-dev0 following x.y.z release"
+tbump X.Y.Z+1-dev0 --no-tag --no-push # You can interrupt during copyrite
+git commit -am "Upgrade the version to x.y.z+1-dev0 following x.y.z release"
 ```
 
 Check the result and then upgrade the master branch

tbump.toml

@@ -1,7 +1,7 @@
 github_url = "https://github.com/PyCQA/astroid"
 
 [version]
-current = "2.7.0-dev0"
+current = "2.6.2-dev0"
 regex = '''
 ^(?P<major>0|[1-9]\d*)
 \.