Don't cache packages on the filesystem

Should help with transient errors reported in #86, #104, and #110

package.json

@@ -21,14 +21,11 @@
     "isomorphic-fetch": "^2.2.1",
     "jsonwebtoken": "^8.1.0",
     "mime": "^1.4.0",
-    "mkdirp": "^0.5.1",
     "morgan": "^1.8.1",
     "ndjson": "^1.5.0",
     "node-forge": "^0.7.1",
-    "os-tmpdir": "^1.0.2",
     "pretty-bytes": "^3",
     "prop-types": "^15.5.8",
-    "proper-lockfile": "^3.0.2",
     "raven": "^2.6.3",
     "react": "^15.5.4",
     "react-dom": "^15.5.4",
@@ -36,8 +33,9 @@
     "react-router-dom": "^4.0.0",
     "redis": "^2.7.1",
     "semver": "^5.3.0",
+    "sort-by": "^1.2.0",
     "sri-toolbox": "^0.2.0",
-    "tar-fs": "^1.16.2",
+    "tar-stream": "^1.6.1",
     "throng": "^4.0.0",
     "validate-npm-package-name": "^3.0.0",
     "warning": "^3.0.0",