diff --git a/README.md b/README.md
index 8842d25..bd8544f 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,7 @@
 
 [![Build Status](https://travis-ci.com/arundo/adtk.svg?branch=master)](https://travis-ci.com/arundo/adtk)
 [![Docs](https://readthedocs.com/projects/arundo-adtk/badge/?version=stable)](https://arundo-adtk.readthedocs-hosted.com)
-[![Coverage Status](https://coveralls.io/repos/github/arundo/adtk/badge.svg?branch=master)](https://coveralls.io/github/arundo/adtk?branch=master)
+[![Coverage Status](https://coveralls.io/repos/github/arundo/adtk/badge.svg?branch=master&service=github)](https://coveralls.io/github/arundo/adtk?branch=master)
 [![PyPI](https://img.shields.io/pypi/v/adtk)](https://pypi.org/project/adtk/)
 [![Downloads](https://pepy.tech/badge/adtk)](https://pepy.tech/project/adtk)
 [![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black)
diff --git a/docs/conf.py b/docs/conf.py
index dea6234..44c5127 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -56,7 +56,7 @@
 
 # General information about the project.
 project = "ADTK"
-copyright = "2019, Arundo Analytics, Inc."
+copyright = "2019-2020, Arundo Analytics, Inc."
 author = "Arundo Analytics, Inc"
 
 # The version info for the project you're documenting, acts as replacement for
@@ -66,7 +66,7 @@
 # The short X.Y version.
 version = "0.5"
 # The full version, including alpha/beta/rc tags.
-release = "0.5.0"
+release = "0.5.1"
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.
diff --git a/docs/releasehistory.rst b/docs/releasehistory.rst
index 7a489b3..94feed3 100644
--- a/docs/releasehistory.rst
+++ b/docs/releasehistory.rst
@@ -2,6 +2,17 @@
 Release History
 ***************
 
+Version 0.5.1 (Jan 2, 2020)
+===================================
+- Added many new unit tests, and modified some old unit test
+- Removed seaborn from dependencies (use matplotlib built-in style now)
+- Fixed a bug in the metric module of dict objects as input
+- Fixed a bug in the detector OutlierDetector that output series has dtype object if NaN is present
+- Fixed a bug in transformer pipeline that detect and transform methods are confused
+- Fixed a bug in pipenet that an aggregator node may crash if its input is from a node where subset contains a single item
+- Fixed a bug in pipenet summary that subset column are always "all" even if not
+- Some minor optimization of code
+
 Version 0.5.0 (Dec 18, 2019)
 ===================================
 - Changed the parameter `steps` of pipenet from list to dict
diff --git a/setup.cfg b/setup.cfg
index 2dcd6ae..1a9ee04 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -1,6 +1,6 @@
 [metadata]
 name = adtk
-version = 0.5.0
+version = 0.5.1
 author = Arundo Analytics, Inc.
 maintainer = Tailai Wen
 maintainer_email = tailai.wen@arundo.com
diff --git a/src/adtk/__init__.py b/src/adtk/__init__.py
index 4197f39..50f0cef 100644
--- a/src/adtk/__init__.py
+++ b/src/adtk/__init__.py
@@ -36,4 +36,4 @@
 # Dev branch marker is: 'X.Y.dev' or 'X.Y.devN' where N is an integer.
 # 'X.Y.dev0' is the canonical version of 'X.Y.dev'
 #
-__version__ = "0.5"
+__version__ = "0.5.1"
diff --git a/tox.ini b/tox.ini
index 1399623..f123e79 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,14 +1,12 @@
 [tox]
-envlist = 
-    py35-pandas{23,24}-numpy{15,16,17}-stats{9,10}
-    py{36,37}-pandas{23,24,25}-numpy{15,16,17}-stats{9,10}
+envlist =
+    py35-pandas24-numpy{16,17}-stats{9,10}
+    py{36,37}-pandas{24,25}-numpy{16,17}-stats{9,10}
 [testenv]
-deps = 
+deps =
     pytest
-    pandas23: pandas>=0.23,<0.24
     pandas24: pandas>=0.24,<0.25
     pandas25: pandas>=0.25,<0.26
-    numpy15: numpy>=1.15,<1.16
     numpy16: numpy>=1.16,<1.17
     numpy17: numpy>=1.17,<1.18
     stats9: statsmodels>=0.9,<0.10