Fix "occured" typo

Author: szepeviktor

README.md

@@ -441,7 +441,7 @@ try {
     $responses = await($promise);
     // responses successfully received
 } catch (Exception $e) {
-    // an error occured while performing the requests
+    // an error occurred while performing the requests
 }
 ```
 

examples/02-http-all.php

@@ -29,7 +29,7 @@ function ($responses) {
         }
     },
     function ($e) {
-        echo 'An error occured: ' . $e->getMessage() . PHP_EOL;
+        echo 'An error occurred: ' . $e->getMessage() . PHP_EOL;
     }
 );
 

examples/03-http-any.php

@@ -31,7 +31,7 @@ function ($url) {
         echo 'First successful URL is ' . $url . PHP_EOL;
     },
     function ($e) {
-        echo 'An error occured: ' . $e->getMessage() . PHP_EOL;
+        echo 'An error occurred: ' . $e->getMessage() . PHP_EOL;
     }
 );