add Apps endpoint get /org/:org:/installation

Author: jamiehuson

lib/Github/Api/Apps.php

@@ -66,6 +66,19 @@ public function getInstallation($installation_id)
         return $this->get('/app/installations/'.rawurldecode($installation_id));
     }
 
+    /**
+     * Get an installation of the application for an organization
+     *
+     * @link https://developer.github.com/v3/apps/#get-an-organization-installation
+     *
+     * @param $org An organization
+     * @return array
+     */
+    public function getInstallationForOrganization($org)
+    {
+        return $this->get('/org/'.rawurldecode($org).'/installation');
+    }
+
     /**
      * Delete an installation of the application
      *

test/Github/Tests/Api/AppTest.php

@@ -56,6 +56,22 @@ public function shouldGetInstallationForApplication()
         $this->assertEquals($result, $api->getInstallation('1234'));
     }
 
+    /**
+     * @test
+     */
+    public function shouldGetInstallationForOrganization()
+    {
+        $result = ['installation1'];
+
+        $api = $this->getApiMock();
+        $api->expects($this->once())
+            ->method('get')
+            ->with('/org/1234/installation')
+            ->willReturn($result);
+
+        $this->assertEquals($result, $api->getInstallationForOrganization('1234'));
+    }
+
     /**
      * @test
      */