Don't cache packages on the filesystem

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

server/utils/getContentType.js

@@ -0,0 +1,22 @@
+const mime = require("mime");
+
+mime.define({
+  "text/plain": [
+    "authors",
+    "changes",
+    "license",
+    "makefile",
+    "patents",
+    "readme",
+    "ts",
+    "flow"
+  ]
+});
+
+const textFiles = /\/?(\.[a-z]*rc|\.git[a-z]*|\.[a-z]*ignore|\.lock)$/i;
+
+function getContentType(file) {
+  return textFiles.test(file) ? "text/plain" : mime.lookup(file);
+}
+
+module.exports = getContentType;