Fix typo

Author: gaearon

beta/src/pages/apis/usecontext.md

@@ -1329,7 +1329,7 @@ Call `useContext` at the top level of your component to read and subscribe to [c
 import { useContext } from 'react';
 
 function MyComponent() {
-  const theme = useTheme(ThemeContext);
+  const theme = useContext(ThemeContext);
   // ...
 ```
 
@@ -1392,4 +1392,4 @@ In both of these cases you should see a warning from React in the console. To fi
 </ThemeContext.Provider>
 ```
 
-Note that the [default value from your `createContext(defaultValue)` call](#specifying-a-fallback-default-value) is only used **if there is no matching provider above at all.** If there is a `<SomeContext.Provider value={undefined}>` component somewhere in the parent tree, the component calling `useContext(SomeContext)` *will* receive `undefined` as the context value.
+Note that the [default value from your `createContext(defaultValue)` call](#specifying-a-fallback-default-value) is only used **if there is no matching provider above at all.** If there is a `<SomeContext.Provider value={undefined}>` component somewhere in the parent tree, the component calling `useContext(SomeContext)` *will* receive `undefined` as the context value.