fix React hook warnings (#57)

Author: VasilyStrelyaev

Diff for: src/components/theme-switcher/ThemeSwitcher.js

@@ -7,7 +7,7 @@ export const ThemeSwitcher = () => {
 
   const onButtonClick = useCallback(() => {
     themeContext?.switchTheme();
-  }, []);
+  }, [themeContext]);
 
   return <div>
             <Button

Diff for: src/theme.js

@@ -45,7 +45,7 @@ export function useThemeContext() {
     document.body.classList.add(themeClassNamePrefix + theme);
   }
 
-  return useMemo(()=> ({ theme, switchTheme, isDark }), [theme]);
+  return useMemo(()=> ({ theme, switchTheme, isDark }), [theme, switchTheme, isDark]);
 }
 
 export const ThemeContext = React.createContext(null);