fix(@schematics/update): replace environment variables in npm/yarn rc

Author: clydin

packages/schematics/update/update/npm.ts

@@ -68,6 +68,11 @@ function readOptions(yarn = false): { [key: string]: string } {
     }
   }
 
+  // Substitute any environment variable references
+  for (const key in options) {
+    options[key] = options[key].replace(/\$\{([^\}]+)\}/, (_, name) => process.env[name] || '');
+  }
+
   return options;
 }