fix(@schematics/update): ensure option is string when replacing environment variable references

When substituting environment variables in npmrc options, string replace was also applied on boolean values. This caused the ng update process to fail

Author: joeson1

packages/schematics/update/update/npm.ts

@@ -84,7 +84,9 @@ function readOptions(
 
   // Substitute any environment variable references
   for (const key in options) {
-    options[key] = options[key].replace(/\$\{([^\}]+)\}/, (_, name) => process.env[name] || '');
+    if (typeof options[key] === 'string') {
+      options[key] = options[key].replace(/\$\{([^\}]+)\}/, (_, name) => process.env[name] || '');
+    }
   }
 
   return options;