tools: add babel-eslint

Create tools/update-babel-eslint.sh script and execute it to do the
first installation of the package.
Update tools/license-builder.sh and execute it to add babel-eslint's
license to our LICENSE file.

PR-URL: #17820
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

LICENSE

@@ -1061,6 +1061,32 @@ The externally maintained libraries used by Node.js are:
     THE SOFTWARE.
   """
 
+- babel-eslint, located at tools/node_modules/babel-eslint, is licensed as follows:
+  """
+    Copyright (c) 2014-2016 Sebastian McKenzie <sebmck@gmail.com>
+
+    MIT License
+
+    Permission is hereby granted, free of charge, to any person obtaining
+    a copy of this software and associated documentation files (the
+    "Software"), to deal in the Software without restriction, including
+    without limitation the rights to use, copy, modify, merge, publish,
+    distribute, sublicense, and/or sell copies of the Software, and to
+    permit persons to whom the Software is furnished to do so, subject to
+    the following conditions:
+
+    The above copyright notice and this permission notice shall be
+    included in all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+    NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+    LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+    OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+    WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+  """
+
 - gtest, located at deps/gtest, is licensed as follows:
   """
     Copyright 2008, Google Inc.

tools/license-builder.sh

@@ -77,6 +77,7 @@ addlicense "marked" "tools/doc/node_modules/marked" \
 addlicense "cpplint.py" "tools/cpplint.py" \
            "$(sed -e '/^$/,$d' -e 's/^#$//' -e 's/^# //' ${rootdir}/tools/cpplint.py | tail -n +3)"
 addlicense "ESLint" "tools/node_modules/eslint" "$(cat ${rootdir}/tools/node_modules/eslint/LICENSE)"
+addlicense "babel-eslint" "tools/node_modules/babel-eslint" "$(cat ${rootdir}/tools/node_modules/babel-eslint/LICENSE)"
 addlicense "gtest" "deps/gtest" "$(cat ${rootdir}/deps/gtest/LICENSE)"
 
 # nghttp2