Fixed: prevent JSPM to throw unrecoverable error (#205)

Closes #198 

Works around jspm/jspm#1779 stuntil that is fixed

Author: swernerx

lib/resolve-id.js

@@ -1,5 +1,11 @@
 var resolve = require("resolve")
-var jspmResolve = require("pkg-resolve")
+var jspmResolve
+try {
+  jspmResolve = require("pkg-resolve")
+}
+catch (ex) {
+  // pass
+}
 
 var moduleDirectories = [
   "web_modules",