Fix: Use nextProps argument in shouldComponentUpdate

The shouldComponentUpdate API defines that the arguments are
nextProps and nextState. So we replace prevProps with nextProps.

Author: markusguenther

src/components/themr.js

@@ -151,12 +151,12 @@ export default (componentName, localTheme, options = {}) => ThemedComponent => {
       return composeTheme ? this.getTheme() : this.getThemeNotComposed()
     }
 
-    shouldComponentUpdate(prevProps) {
+    shouldComponentUpdate(nextProps) {
       const { composeTheme, theme, themeNamespace } = this.props
       if (
-        composeTheme !== prevProps.composeTheme ||
-        theme !== prevProps.theme ||
-        themeNamespace !== prevProps.themeNamespace
+        composeTheme !== nextProps.composeTheme ||
+        theme !== nextProps.theme ||
+        themeNamespace !== nextProps.themeNamespace
       ) {
         this.theme_ = this.calcTheme()
       }