Fix typos

Author: lex111

1-js/10-error-handling/1-try-catch/article.md

@@ -521,7 +521,7 @@ try {
 }
 */!*
 
-alert(result || "error occured");
+alert(result || "error occurred");
 
 alert( `execution took ${diff}ms` );
 ```

10-misc/12-mutation-observer/article.md

@@ -38,7 +38,7 @@ Then after any changes, the `callback` is executed, with a list of [MutationReco
     - `"attributes"`: attribute modified
     - `"characterData"`: data modified, used for text nodes,
     - `"childList"`: child elements added/removed,
-- `target` -- where the change occured: an element for "attributes", or text node for "characterData", or an element for a "childList" mutation,
+- `target` -- where the change occurred: an element for "attributes", or text node for "characterData", or an element for a "childList" mutation,
 - `addedNodes/removedNodes`  -- nodes that were added/removed,
 - `previousSibling/nextSibling` -- the previous and next sibling to added/removed nodes,
 - `attributeName/attributeNamespace` -- the name/namespace (for XML) of the changed attribute,

2-ui/5-loading/03-onload-onerror/article.md

@@ -92,7 +92,7 @@ img.onload = function() {
 };
 
 img.onerror = function() {
-  alert("Error occured while loading image");
+  alert("Error occurred while loading image");
 };
 ```
 

4-binary/04-file/article.md

@@ -60,7 +60,7 @@ As the reading proceeds, there are events:
 - `progress` -- occurs during reading.
 - `load` -- no errors, reading complete.
 - `abort` -- `abort()` called.
-- `error` -- error has occured.
+- `error` -- error has occurred.
 - `loadend` -- reading finished with either success or failure.
 
 When the reading is finished, we can access the result as:

5-network/07-xmlhttprequest/article.md

@@ -495,7 +495,7 @@ There are actually more events, the [modern specification](http://www.w3.org/TR/
 - `loadstart` -- the request has started.
 - `progress` -- a data packet of the response has arrived, the whole response body at the moment is in `responseText`.
 - `abort` -- the request was canceled by the call `xhr.abort()`.
-- `error` -- connection error has occured, e.g. wrong domain name. Doesn't happen for HTTP-errors like 404.
+- `error` -- connection error has occurred, e.g. wrong domain name. Doesn't happen for HTTP-errors like 404.
 - `load` -- the request has finished successfully.
 - `timeout` -- the request was canceled due to timeout (only happens if it was set).
 - `loadend` -- the request has finished (succeffully or not).