More accurate PHP version compatibility info

see https://community.haxe.org/t/what-version-of-php-7-does-haxe-generate/1570/8
[skip ci]

README.md

@@ -89,7 +89,7 @@ Haxe            | Neko  | SWF |  Python   | HL    | PHP   | Lua  |
 3.0.0           | 2.0.0 |        | -      | -     | 5.1+  | -    |
 3.2.0           |       | 12-14  | 3.2+   | -     |       | -    |
 3.3.0           | 2.1.0 | 21     |        | -     |       | 5.1, 5.2, 5.3, LuaJIT 2.0, LuaJIT 2.1 |
-3.4.0           |       |        |        | 1.1   | 5.1 and 7.0 (with `-D php7`)   |      |
+3.4.0           |       |        |        | 1.1   | 5.4+ and 7.0+ (with `-D php7`)   |      |
 4.0.0 preview 1 |       |        |        | 1.2   | 7.0+  |      |
 4.0.0 preview 3 |       |        |        | 1.3   |       |      |
 4.0.0 preview 4 |       |        |        | 1.6   |       |      |