Update schema description for sub-domain part

Corrected the grammar in the schema description for clarity. Changed "It is just the sub-domain part." to "it's just the sub-domain part." to ensure proper use of the contraction.

src/main/java/codes/thischwa/dyndrest/AdminRoutes.java

@@ -151,7 +151,7 @@ ResponseEntity<Void> addHost(
           @PathVariable
           String zoneName,
       @Schema(
-              description = "The name of the host to create, It is just the sub-domain part.",
+              description = "The name of the host to create, it's just the sub-domain part.",
               type = "string",
               example = "host1")
           @PathVariable