Update README.md

README.md

@@ -24,7 +24,7 @@ If your code does compile without these two options but does not compile with th
 
 A sample invocation of the command:
 
-`g++ src/sample_4.cpp -o sample_4 -std=c++11 -Wall -Werr`
+`g++ src/sample_4.cpp -o sample_4 -std=c++11 -Wall -Werror`
 
 And the sample program can then be run by calling