Add an explicit warning if the path-to-regexp version is wrong

package.json

@@ -33,7 +33,6 @@
   "dependencies": {
     "babel-runtime": "^6.23.0",
     "farce": "^0.2.1",
-    "invariant": "^2.2.2",
     "is-promise": "^2.1.0",
     "lodash": "^4.17.4",
     "path-to-regexp": "^1.7.0",

src/Matcher.js

@@ -1,9 +1,19 @@
 import isEqual from 'lodash/isEqual';
 import pathToRegexp from 'path-to-regexp';
+import warning from 'warning';
 
 export default class Matcher {
   constructor(routeConfig) {
     this.routeConfig = routeConfig;
+
+    // Overly-aggressive deduplication of packages can lead to the wrong
+    // version of path-to-regexp getting bundled. This is a common enough
+    // failure mode that it's worthwhile to add a dev-only warning here.
+    warning(
+      typeof pathToRegexp.compile === 'function',
+      'Incorrect version of path-to-regexp imported. If this is running ' +
+      'from a client bundle, check your bundler settings.',
+    );
   }
 
   match({ pathname }) {