fix: typo in bridge accuracy

Also corrected the macro-average.

README.md

@@ -211,9 +211,9 @@ The following table gives the class-wise metrics on the test set:
 **vegetation**|93.8|95.6|98.0|95.6|96.8
 **building**|90.4|93.7|96.2|93.7|95.0
 **water**|90.1|92.6|97.1|92.6|94.8
-**bridge**|65.2|96.1|79.3|78.6|79.0
+**bridge**|65.2|78.6|79.3|78.6|79.0
 **permanent structure**|63.5|76.6|78.9|76.6|77.7
-**Macro Average**|77.5|86.7|88.7|84.2|86.2
+**Macro Average**|77.5|84.2|88.7|84.2|86.2
 
 
 The following illustration gives the resulting confusion matrix :