Update ruby to 2.5.1 (#583)

* Update ruby to 2.5.1

* Update bundler before installing

.ruby-version

@@ -1 +1 @@
-2.5.0
+2.5.1

.travis.yml

@@ -1,10 +1,11 @@
 language: ruby
 sudo: false
 rvm:
-  - 2.5.0
+  - 2.5.1
 
 before_install:
   - gem update --system
+  - gem install bundler
 
 services:
   - postgresql

Dockerfile

@@ -1,4 +1,4 @@
-FROM ruby:2.5.0-alpine
+FROM ruby:2.5.1-alpine
 RUN apk add --update \
   build-base \
   netcat-openbsd \

Gemfile

@@ -1,5 +1,5 @@
 source 'https://rubygems.org'
-ruby '2.5.0'
+ruby '2.5.1'
 
 gem 'rails', '~> 5.1'
 gem 'bootstrap-sass'

Gemfile.lock

@@ -346,7 +346,7 @@ DEPENDENCIES
   webmock
 
 RUBY VERSION
-   ruby 2.5.0p0
+   ruby 2.5.1p57
 
 BUNDLED WITH
    1.16.1

INSTALLATION.md

@@ -60,13 +60,13 @@ Please refer to the separate [OpenShift installation](openshift/OPENSHIFT_INSTAL
 
 ## Local installation
 
-First things first, you'll need to install Ruby 2.5.0. I recommend using the excellent [rbenv](https://github.com/rbenv/rbenv),
+First things first, you'll need to install Ruby 2.5.1. I recommend using the excellent [rbenv](https://github.com/rbenv/rbenv),
 and [ruby-build](https://github.com/rbenv/ruby-build):
 
 ```bash
 brew install rbenv ruby-build
-rbenv install 2.5.0
-rbenv global 2.5.0
+rbenv install 2.5.1
+rbenv global 2.5.1
 ```
 
 Next, you'll need to make sure that you have PostgreSQL installed. This can be