fix travis build

.ruby-version

@@ -1 +1 @@
-2.5.0
+2.5.7

.travis.yml

@@ -1,7 +1,11 @@
 sudo: required
+before_install:
+  - sudo apt-get -y install curl
 
 language: ruby
-cache: bundler
+rvm: 2.5.7
+install:
+  - rvm use 2.5.7 --install
 
 services:
   - docker

Dockerfile

@@ -1,4 +1,4 @@
-FROM ruby:2.5
+FROM ruby:2.5.7
 RUN curl -sL https://deb.nodesource.com/setup_9.x | bash - && apt-get update && \
   apt-get install -y build-essential zlib1g-dev libsqlite3-dev nodejs npm \
   libxml2-dev libxslt1-dev pkg-config \

Gemfile.lock

@@ -316,6 +316,3 @@ DEPENDENCIES
   tzinfo-data
   uglifier
   validate_url
-
-BUNDLED WITH
-   1.16.1