fix(ci): avoid parallel ipfs.add* on Windows

TravisCI often fails on Windows due to parallel add* of the same data clashing
with the way Node manages fs access on Windows. Switching to one after should
stabilize test suite on Windows by removing surface for those race conditions.

License: MIT
Signed-off-by: Marcin Rataj <lidel@lidel.org>

package.json

@@ -195,7 +195,7 @@
     "execa": "^2.0.4",
     "form-data": "^2.5.1",
     "hat": "0.0.3",
-    "interface-ipfs-core": "^0.113.0",
+    "interface-ipfs-core": "https://github.com/ipfs/interface-js-ipfs-core/tarball/8c83bcec854fb486551c762be6f0c41ba8694cd4/interface-js-ipfs-core.tar.gz",
     "ipfsd-ctl": "~0.46.0",
     "libp2p-websocket-star": "~0.10.2",
     "ncp": "^2.0.0",