fix typo in custom attribute converter tutorial (#1307)

packages/lit-dev-content/site/tutorials/content/custom-attribute-converter/00.md

@@ -1,6 +1,6 @@
 Web Components can receive data in many ways, but one of the most common ways is to use an attribute because attributes are declarative, static, and easy to read & write in HTML!
 
-Every HTML element in the browser has *attibutes* and *properties*:
+Every HTML element in the browser has *attributes* and *properties*:
 
  *   [*Attributes*](https://developer.mozilla.org/en-US/docs/Glossary/attribute) are additional values that describe the state of an element in HTML. Attributes can only have string values.
  *   [*Properties*](https://developer.mozilla.org/en-US/docs/Glossary/property/JavaScript) are the instance properties of an element's JavaScript DOM object. Properties can take any kind of value, like numbers, booleans, and arrays.