diff --git a/.github/workflows/actions.yml b/.github/workflows/actions.yml
new file mode 100644
index 0000000..6a73aaa
--- /dev/null
+++ b/.github/workflows/actions.yml
@@ -0,0 +1,23 @@
+name: CI
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    env:
+      BUNDLE_DEPLOYMENT: "false" # do not fail test when bumping release without bundling
+    strategy:
+      matrix:
+        ruby: [ '2.5', '2.6', '2.7', '3.0' ] # lowest must match ruby version in gemspec
+        task: [ 'default' ]
+    name: ${{ matrix.ruby }} rake ${{ matrix.task }}
+    steps:
+    - uses: actions/checkout@v2
+    - uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby }}
+        bundler-cache: true # runs 'bundle install' and caches installed gems automatically
+    - run: bundle exec rake
diff --git a/.travis.yml b/.travis.yml
deleted file mode 100644
index 06daf0d..0000000
--- a/.travis.yml
+++ /dev/null
@@ -1,13 +0,0 @@
-language: ruby
-cache: bundler
-sudo: false
-branches:
-  only: master
-matrix:
-  fast_finish: true
-rvm:
-  - 2.0.0
-  - 2.1.6
-  - 2.2.4
-  - 2.3.0
-
diff --git a/Gemfile.lock b/Gemfile.lock
index afdc407..7e83b21 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -6,20 +6,21 @@ PATH
 GEM
   remote: https://rubygems.org/
   specs:
-    bump (0.5.0)
-    diff-lcs (1.2.5)
-    rake (10.3.2)
-    rspec (2.14.1)
-      rspec-core (~> 2.14.0)
-      rspec-expectations (~> 2.14.0)
-      rspec-mocks (~> 2.14.0)
-    rspec-core (2.14.8)
-    rspec-expectations (2.14.5)
+    bump (0.10.0)
+    diff-lcs (1.4.4)
+    rake (13.0.6)
+    rspec (2.99.0)
+      rspec-core (~> 2.99.0)
+      rspec-expectations (~> 2.99.0)
+      rspec-mocks (~> 2.99.0)
+    rspec-core (2.99.2)
+    rspec-expectations (2.99.2)
       diff-lcs (>= 1.1.3, < 2.0)
-    rspec-mocks (2.14.6)
+    rspec-mocks (2.99.4)
 
 PLATFORMS
-  ruby
+  x86_64-darwin-19
+  x86_64-linux
 
 DEPENDENCIES
   bump
@@ -28,4 +29,4 @@ DEPENDENCIES
   rspec (~> 2)
 
 BUNDLED WITH
-   1.11.2
+   2.2.16
diff --git a/Readme.md b/Readme.md
index 0127e6b..9215143 100644
--- a/Readme.md
+++ b/Readme.md
@@ -8,8 +8,8 @@ Pipeable Ruby - forget about grep / sed / awk / wc ... use pure, readable Ruby!
     # select lines longer than five letters
     ls -1 | pru 'size > 5'
 
-    # passthrough
-    ls -1 | pru self
+    # 2nd to last character
+    ls -1 | pru self[2..-1]
 
 
 ## Reduce - all lines as Array
@@ -20,8 +20,8 @@ Pipeable Ruby - forget about grep / sed / awk / wc ... use pure, readable Ruby!
     # are the more than five lines?
     ls -1 | pru -r 'size > 5'
 
-    # passthrough
-    ls -1 | pru -r self
+    # get 2nd to last line
+    ls -1 | pru -r self[2..-1]
 
 
 ## Map and Reduce
@@ -117,8 +117,8 @@ Gemsets
 Working with rvm / many gemsets -> only install once
 (or use standalone binary)
 
-    rvm 1.9.2 exec gem install pru
-    echo 'alias pru="rvm 1.9.2 exec pru"' >> ~/.bash_profile
+    rvm 2.7.7 exec gem install pru
+    echo 'alias pru="rvm 2.7.2 exec pru"' >> ~/.bash_profile
 
 
 [Contributors](http://github.com/grosser/pru/contributors)
diff --git a/lib/pru/core_ext/array.rb b/lib/pru/core_ext/array.rb
index 0e4f206..7880f5e 100644
--- a/lib/pru/core_ext/array.rb
+++ b/lib/pru/core_ext/array.rb
@@ -11,8 +11,8 @@ def sum(method = nil, &block)
     end
   end unless method_defined?(:sum)
 
-  def mean(method = nil, &block)
-    sum(method, &block) / size.to_f
+  def mean(*args, &block)
+    sum(*args, &block) / size.to_f
   end unless method_defined?(:mean)
 
   def grouped
diff --git a/pru.gemspec b/pru.gemspec
index bf053a8..84f0b3a 100644
--- a/pru.gemspec
+++ b/pru.gemspec
@@ -10,4 +10,5 @@ Gem::Specification.new name, Pru::VERSION do |s|
   s.files = `git ls-files lib`.split("\n")
   s.license = "MIT"
   s.executables = ["pru"]
+  s.required_ruby_version = '>= 2.5' # must match lowest in .github/workflows/actions.yml
 end