Fix typo in documentation

Author: eyupatis

README.md

@@ -641,7 +641,7 @@ To configure this, use `.at_fork`.
 ```ruby
 SimpleCov.enable_for_subprocesses true
 SimpleCov.at_fork do |pid|
-  # This needs a unique name so it won't be ovewritten
+  # This needs a unique name so it won't be overwritten
   SimpleCov.command_name "#{SimpleCov.command_name} (subprocess: #{pid})"
   # be quiet, the parent process will be in charge of output and checking coverage totals
   SimpleCov.print_error_status = false