Fix display of the month at creation date

client/src/main/kotlin/org/hso/texturesyncclient/controller/net/InternalJsonModel.kt

@@ -50,11 +50,11 @@ internal data class InternalTexture(
                     else -> throw ConnectionInvalidJsonException()
                 },
                 resolution = Pair(resolution[0], resolution[1]),
-                addedOn = GregorianCalendar(added_on[0], added_on[1], added_on[2]),
+                addedOn = GregorianCalendar(added_on[0], added_on[1] - 1, added_on[2]),
                 textureHash = Sha256(texture_hash)
             )
         } catch (e: Exception) { // i Know, but no time :[]
             throw ConnectionInvalidJsonException()
         }
     }
-}
+}