catch empty routes

This fixes a bug where an empty route would catch all requests resulting
in all routes found with the empty route.

lib/zero/router.rb

@@ -40,7 +40,7 @@ module Zero
       routes.each do |route, target|
         @routes[
           Regexp.new(
-            route.gsub(VARIABLE_MATCH, VARIABLE_REGEX) + '$')] = target
+            '^' + route.gsub(VARIABLE_MATCH, VARIABLE_REGEX) + '$')] = target
       end
     end
 

spec/unit/zero/router/call_spec.rb

@@ -25,6 +25,13 @@ describe Zero::Router, '#call' do
     it_behaves_like "a sample app"
   end
 
+  context 'with empty path' do
+    let(:routes) {{ '' => wrong_app, '/welcome' => app }}
+    let(:env) { EnvGenerator.get('/welcome') }
+
+    it_behaves_like "a sample app"
+  end
+
   context 'with multiple router' do
     let(:routes) {{ '/foo' => app, '/wrong' => wrong_app }}
     let(:env) { EnvGenerator.get('/foo') }
@@ -45,6 +52,14 @@ describe Zero::Router, '#call' do
     it_behaves_like "a sample app"
   end
 
+  context 'with empty route' do
+    let(:routes) {{ '' => wrong_app }}
+    let(:env) { EnvGenerator.get('/foo') }
+    let(:result) { ['Not found!'] }
+    let(:status_code) { 404 }
+    it_behaves_like "a sample app"
+  end
+
   context 'with parameters' do
     let(:routes) {{ '/foo/:id' => app }}
     let(:env) { EnvGenerator.get('/foo/bar') }