fix typo

Author: weltling

UPGRADING

@@ -725,7 +725,7 @@ out, that the corresponding SDK isn't available anymore.
 - PDO_Firebird
   As of PHP 7.0.17, the fetched data for integer fields is aware of the Firebird
   datatypes. Previously all integers was fetched as strings, starting with the
-  aforementioned PHP version intger fields are translated to the PHP integer
+  aforementioned PHP version integer fields are translated to the PHP integer
   datatype. The 64-bit integers are still fetched as strings in 32-bit PHP
   builds.