PlatformIO: set build.libArchive to false (closes #1550)

CHANGELOG.md

@@ -18,6 +18,7 @@ HEAD
 * Fixed member-call-on-null-pointer in `getMember()` when array is empty
 * `serializeMsgPack(doc, buffer, size)` doesn't add null-terminator anymore (issue #1545)
 * `serializeJson(doc, buffer, size)` adds null-terminator only if there is enough room
+* PlatformIO: set `build.libArchive` to `false` (PR #1550 by @askreet)
 
 > ### BREAKING CHANGES
 >