Update to use modern RSpec syntax and conventions

* Replace `should` syntax with `expect` syntax.
* Add pry as a development dependency.
* Fix failing specs.

spec/deprecated/cache_config_spec.rb

@@ -18,15 +18,15 @@ describe MusicBrainz::Deprecated::CacheConfig do
   it "allows deprecated use of cache_path" do
     MusicBrainz.config.cache_path = "test1"
 
-    MusicBrainz::Tools::Cache.cache_path.should == "test1"
-    MusicBrainz.cache_path.should == "test1"
+    expect(MusicBrainz::Tools::Cache.cache_path).to eq "test1"
+    expect(MusicBrainz.cache_path).to eq "test1"
   end
 
   it "allows deprecated use of cache_path=" do
     MusicBrainz::Tools::Cache.cache_path = "test2"
-    MusicBrainz.config.cache_path.should == "test2"
+    expect(MusicBrainz.config.cache_path).to eq "test2"
 
     MusicBrainz.cache_path = "test3"
-    MusicBrainz.config.cache_path.should == "test3"
+    expect(MusicBrainz.config.cache_path).to eq "test3"
   end
 end

spec/deprecated/proxy_config_spec.rb

@@ -18,15 +18,15 @@ describe MusicBrainz::Deprecated::ProxyConfig do
   it "allows deprecated use of query_interval" do
     MusicBrainz.config.query_interval = 2
 
-    MusicBrainz::Tools::Proxy.query_interval.should == 2
-    MusicBrainz.query_interval.should == 2
+    expect(MusicBrainz::Tools::Proxy.query_interval).to eq 2
+    expect(MusicBrainz.query_interval).to eq 2
   end
 
   it "allows deprecated use of query_interval=" do
     MusicBrainz::Tools::Proxy.query_interval = 3
-    MusicBrainz.config.query_interval.should == 3
+    expect(MusicBrainz.config.query_interval).to eq 3
 
     MusicBrainz.query_interval = 4
-    MusicBrainz.config.query_interval.should == 4
+    expect(MusicBrainz.config.query_interval).to eq 4
   end
 end