Update templates to use Addressable::URI

Ports swagger-api/swagger-codegen#10445.

src/main/resources/ruby-client/client.mustache

@@ -7,7 +7,7 @@ require 'json'
 require 'logger'
 require 'tempfile'
 require 'typhoeus'
-require 'uri'
+require 'addressable/uri'
 
 module {{moduleName}}
   module API
@@ -56,7 +56,7 @@ module {{moduleName}}
                               :message => response.return_message)
           else
             fail API::Error.new(:code => response.code,
-                              :response_headers => response.headers,
+                              :response_headers => response.headers.to_h,
                               :response_body => response.body),
                  response.status_message
           end
@@ -264,7 +264,7 @@ module {{moduleName}}
       def build_request_url(path)
         # Add leading and trailing slashes to path
         path = "/#{path}".gsub(/\/+/, '/')
-        URI.encode(@config.base_url + path)
+        Addressable::URI.encode(@config.base_url + path)
       end
 
       # Builds the HTTP request body

src/main/resources/ruby-client/configuration.mustache

@@ -2,7 +2,7 @@
 {{> api_info}}
 =end
 
-require 'uri'
+require 'addressable/uri'
 
 module {{moduleName}}
   module API
@@ -168,7 +168,7 @@ module {{moduleName}}
 
       def base_url
         url = "#{scheme}://#{[host, base_path].join('/').gsub(/\/+/, '/')}".sub(/\/+\z/, '')
-        URI.encode(url)
+        Addressable::URI.encode(url)
       end
 
       # Gets API key (with prefix if set).

src/main/resources/ruby-client/gemspec.mustache

@@ -31,4 +31,5 @@ Gem::Specification.new do |s|
 
   s.add_runtime_dependency 'typhoeus', '~> 1.0', '>= 1.0.1'
   s.add_runtime_dependency 'json', '~> 2.1', '>= 2.1.0'
+  s.add_runtime_dependency 'addressable', '~> 2.3', '>= 2.3.0'
 end