Island: Do not allow Windows ransomware target paths beginning with "$"

As far as I can tell, environment variables in Windows look like %NAME%.
Variables in powershell begin with $, but file explorer doesn't
recognize paths beginning with $ as valid.

monkey/monkey_island/cc/ui/src/components/configuration-components/ValidationFormats.js

@@ -11,7 +11,7 @@ const linuxPathStartsWithTildeRegex = /^~/ // path starts with `~`
 const windowsAbsolutePathRegex = /^([A-Za-z]:(\\|\/))/ // path starts like `C:\` OR `C:/`
 const windowsEnvVarNonNumeric = '[A-Za-z#\\$\'\\(\\)\\*\\+,-\\.\\?@\\[\\]_`\\{\\}~+ ]'
 const windowsPathStartsWithEnvVariableRegex = new RegExp(
-	`^\\$|^%(${windowsEnvVarNonNumeric}+(${windowsEnvVarNonNumeric}|\\d)*)%`
+	`^%(${windowsEnvVarNonNumeric}+(${windowsEnvVarNonNumeric}|\\d)*)%`
 );// path starts like `$` OR `%abc%`
 
 const emptyRegex = /^$/