Changed "Javascript interpreter" to "Javascript engine"

I think the phrase "Javascript engine" is more accurate than "Javascript interpreter" because certain Javascript engines, like the V8 engine used in Google Chrome, convert Javascript directly into machine code and do not utilize an interpreter at all.

Source: https://developers.google.com/v8/design - Check the section titled "Dynamic Machine Code Generation"

README.rst

@@ -541,7 +541,7 @@ The components of the browsers are:
   boxes and windows. This backend exposes a generic interface that is not
   platform specific.
   Underneath it uses operating system user interface methods.
-* **JavaScript interpreter:** The JavaScript interpreter is used to parse and
+* **JavaScript engine:** The JavaScript engine is used to parse and
   execute JavaScript code.
 * **Data storage:** The data storage is a persistence layer. The browser may
   need to save all sorts of data locally, such as cookies. Browsers also