Prepare 1.8

ChangeLog

@@ -4,6 +4,8 @@ Pylint's ChangeLog
 What's New in Pylint 1.8?
 =========================
+Release date: 2017-12-15
+
     * Respect disable=... in config file when running with --py3k.
     * New warning `shallow-copy-environ` added

doc/whatsnew/1.7.rst

@@ -2,7 +2,7 @@
   What's New In Pylint 1.7
 **************************
-:Release: |release|
+:Release: 1.7
 :Date: 2017-04-13

doc/whatsnew/1.8.rst

@@ -2,8 +2,8 @@
   What's New In Pylint 1.8
 **************************
-:Release: |release|
-:Date: |TBA|
+:Release: 1.8
+:Date: 2017-12-15
 Summary -- Release highlights

pylint/__pkginfo__.py

@@ -22,7 +22,7 @@ numversion = (1, 8, 0)
 version = '.'.join([str(num) for num in numversion])
 install_requires = [
-    'astroid>=1.5.1',
+    'astroid<2.0',
     'six',
     'isort >= 4.2.5',
     'mccabe',