test: use service alias 'altertable' instead of 127.0.0.1 in CI

Author: Albert

spec/altertable_spec.rb

@@ -4,10 +4,10 @@
 
 RSpec.describe Altertable do
   let(:api_key) { "pk_test_123" }
-  let(:base_url) { "http://127.0.0.1:15000" }
+  let(:base_url) { "http://altertable:15000" }
 
   before do
-    Altertable.init(api_key, base_url: 'http://127.0.0.1:15000')
+    Altertable.init(api_key, base_url: 'http://altertable:15000')
   end
 
   it "has a version number" do