Fixed "substract" is a misspelling of "subtract"

src/Database/FunctionsBuilder.php

@@ -195,7 +195,7 @@ class FunctionsBuilder
      * Add the time unit to the date expression
      *
      * @param string $expression Expression to obtain the date part from.
-     * @param string $value Value to be added. Use negative to substract.
+     * @param string $value Value to be added. Use negative to subtract.
      * @param string $unit Unit of the value e.g. hour or day.
      * @param array $types list of types to bind to the arguments
      * @return \Cake\Database\Expression\FunctionExpression