Fix typos in documentation and examples

Author: yadaiio

README.md

@@ -169,7 +169,7 @@ try {
     $results = await($promise);
     // results successfully received
 } catch (Exception $e) {
-    // an error occured while performing the request
+    // an error occurred while performing the request
 }
 ```
 

examples/exec-stream.php

@@ -27,7 +27,7 @@
 $out = new React\Stream\WritableResourceStream(STDOUT);
 $stderr = new React\Stream\WritableResourceStream(STDERR);
 
-// unkown exit code by default
+// unknown exit code by default
 $exit = 1;
 
 $client->execCreate($container, $cmd)->then(function ($info) use ($client, $out, $stderr, &$exit) {

examples/logs.php

@@ -27,7 +27,7 @@ function ($logs) {
     },
     function (Exception $e) use ($container) {
         echo <<<EOT
-An error occured while trying to access the logs.
+An error occurred while trying to access the logs.
 
 Have you tried running the following command?