Update README.md

There was a mistake in the formula for EVI in the general description. Fixed that.

sentinel-2/evi/README.md

@@ -28,7 +28,7 @@ examples:
 
 For Sentinel-2, the index looks like this:
 
-$$EVI = 2.5 \cdot (\frac{B8-B4}{B8+6 \cdot B6-7.5 \cdot B2} + 1)$$ 
+$$EVI = 2.5 \cdot (\frac{B8-B4}{B8+6 \cdot B4-7.5 \cdot B2} + 1)$$ 
 
 In areas of dense canopy cover, where leaf area index (LAI) is high, the blue wavelengths can be used to improve the accuracy of NDVI, as it corrects for soil background signals and atmospheric influences.