Update dependency to rake and rspec, drop support for Ruby 1.8.7

.travis.yml

@@ -5,5 +5,8 @@ before_script:
   - git config --global user.name "John Doe"
 rvm:
   - 1.9.3
-  - 2.1.5
-  - 2.2.0
+  - 2.1.10
+  - 2.2.7
+  - 2.3.4
+  - 2.4.1
+

pkgr.gemspec

@@ -8,7 +8,7 @@ Gem::Specification.new do |s|
   s.name                      = "pkgr"
   s.version                   = Pkgr::VERSION
   s.platform                  = Gem::Platform::RUBY
-  s.required_ruby_version     = '>= 1.8.7'
+  s.required_ruby_version     = '>= 1.9.3'
   s.required_rubygems_version = ">= 1.3"
   s.authors                   = ["Cyril Rohr"]
   s.email                     = ["cyril.rohr@gmail.com"]
@@ -19,13 +19,13 @@ Gem::Specification.new do |s|
 
   s.license = 'MIT'
 
-  s.add_dependency('rake', '~> 10.0')
+  s.add_dependency('rake', '~> 12.2.1') # rake 12.3 requires ruby 2.x
   s.add_dependency('thor', '~> 0.19')
   s.add_dependency('fpm', '~> 1.1')
   s.add_dependency('facter', '~> 2.1')
   s.add_dependency('mixlib-log', '~> 1.6')
   s.add_dependency('mixlib-shellout', '~> 1.4')
-  s.add_development_dependency('rspec', '~> 2')
+  s.add_development_dependency('rspec', '~> 3')
 
   s.files = Dir.glob("{lib,data}/**/*") + %w(LICENSE README.md)