[lib] Minor method name fix in variable fonts activity

Author: mta452

demo/src/main/java/com/mta/tehreer/demo/VariableFontsActivity.java

@@ -200,6 +200,6 @@ private void setupTypeface(Typeface typeface) {
 
     private void setupCoordinate(int axisIndex, float coordinate) {
         mVariationCoordinates[axisIndex] = coordinate;
-        setupTypeface(mTypeface.deriveVariation(mVariationCoordinates));
+        setupTypeface(mTypeface.getVariationInstance(mVariationCoordinates));
     }
 }