Build: upgrade to latest stable ruby

Author: harding

.ruby-version

@@ -1 +1 @@
-2.5.1
+2.6.4

.travis.yml

@@ -1,7 +1,7 @@
 dist: xenial
 language: ruby
 rvm:
-  - "2.5.1"
+  - "2.6.4"
 
 ## Allows use of docker-based containers, which are more available than
 ## the xen-based (or whatever) VMs, so builds tend to happen sooner

Gemfile

@@ -3,7 +3,7 @@ source 'https://rubygems.org'
 ## If you update the version here, also update it in .travis.yml, .ruby-version,
 ## and README.md. Then push your branch and make sure Travis supports that
 ## version.
-ruby '2.5.1'
+ruby '2.6.4'
 
 ## If you add a new Gem below, run `bundle install` to install it.
 group :development do

Gemfile.lock

@@ -105,7 +105,7 @@ DEPENDENCIES
   minima (~> 2.0)
 
 RUBY VERSION
-   ruby 2.5.1p57
+   ruby 2.6.4p104
 
 BUNDLED WITH
-   1.16.6
+   1.17.3

README.md

@@ -37,19 +37,19 @@ following command:
 
     source ~/.rvm/scripts/rvm
 
-**Install Ruby 2.5.1**
+**Install Ruby**
 
-To install Ruby 2.5.1, simply run this command:
+To install Ruby 2.6.4, simply run this command:
 
-    rvm install 2.5.1
+    rvm install 2.6.4
 
 Sometimes this will find a pre-compiled Ruby package for your Linux
 distribution, but sometimes it will need to compile Ruby from scratch
 (which takes about 15 minutes).
 
-After Ruby 2.5.1 is installed, make it your default Ruby:
+After Ruby 2.6.4 is installed, make it your default Ruby:
 
-    rvm alias create default ruby-2.5.1
+    rvm alias create default ruby-2.6.4
 
 And tell your system to use it:
 
@@ -106,12 +106,9 @@ sure you're in the `bitcoinops.github.io` directory and run:
     make
 
 The resulting HTML for the entire site will be placed in the `_site`
-directory.  The following alternative options are available:
-
-    ## After you build the site, you can run all of the tests (may take awhile)
-    make test
+directory and various tests will be run.
 
 ## Contributing
 
 If you would like to contribute to the Bitcoin Optech project, please review the
-[contributing guidelines](CONTRIBUTING.md).
+[contributing guidelines](CONTRIBUTING.md).