Travis: work around Bundler

Bundler did drop support for MRI 2.2, which we still want
to support. Sometime I feel like they do these things on
purpose...

Author: dmke

bin/travis.sh

@@ -9,5 +9,5 @@ else
 	gem update --system --no-doc
 fi
 
-gem install bundler --no-doc
-gem update bundler --no-doc
+# Bundler 2.0 fails spectacular
+gem install bundler --no-doc --version '< 2'

influxdb.gemspec

@@ -18,7 +18,7 @@ Gem::Specification.new do |spec|
 
   spec.required_ruby_version = ">= 2.2.0"
 
-  spec.add_development_dependency "bundler", "~> 1.3"
+  spec.add_development_dependency "bundler", "< 2"
   spec.add_development_dependency "rake"
   spec.add_development_dependency "rspec", "~> 3.6"
   spec.add_development_dependency "rubocop", "~> 0.61.1"