Fix typo

README.md

@@ -73,7 +73,7 @@ stack install --fast
 ihaskell install --stack
 ```
 
-If you have Homebrew installed to a custom location, you'd need to specify `--extra-include-dirs ${HOMEBREW_PREFIX}/include ----extra-lib-dir ${HOMEBREW_PREFIX}/lib` to the `stack` command. 
+If you have Homebrew installed to a custom location, you'd need to specify `--extra-include-dirs ${HOMEBREW_PREFIX}/include --extra-lib-dir ${HOMEBREW_PREFIX}/lib` to the `stack` command. 
 
 Run Jupyter.