Fix PHP 5 compat in CertificateStore

composer.json

@@ -1,6 +1,15 @@
 {
     "name": "kelunik/acme-client",
     "description": "Standalone PHP ACME client.",
+    "keywords": [
+        "ACME",
+        "letsencrypt",
+        "certificate",
+        "https",
+        "encryption",
+        "ssl",
+        "tls"
+    ],
     "require": {
         "amphp/process": "^0.1.1",
         "bramus/monolog-colored-line-formatter": "^2",

src/Stores/CertificateStore.php

@@ -2,6 +2,7 @@
 
 namespace Kelunik\AcmeClient\Stores;
 
+use Amp\CoroutineResult;
 use Amp\File\FilesystemException;
 use InvalidArgumentException;
 use Kelunik\Certificate\Certificate;
@@ -26,7 +27,8 @@ class CertificateStore {
         Assert::string($name, "Name must be a string. Got: %s");
 
         try {
-            return yield \Amp\File\get($this->root . "/" . $name . "/cert.pem");
+            $contents = (yield \Amp\File\get($this->root . "/" . $name . "/cert.pem"));
+            yield new CoroutineResult($contents);
         } catch (FilesystemException $e) {
             throw new CertificateStoreException("Failed to load certificate.", 0, $e);
         }
@@ -88,4 +90,4 @@ class CertificateStore {
 
         yield \Amp\File\rmdir($this->root . "/" . $name);
     }
-}
+}