Warn when a shrinkwrap exists in the cwd (#397)

* warn when a shrinkwrap exists in the cwd - fixes #396

* Wrap TODO with brackets

Author: Sebastian McKenzie

src/cli/commands/install.js

@@ -199,6 +199,11 @@ export class Install {
     // remove integrity hash to make this operation atomic
     await fs.unlink(match.loc);
 
+    // warn if we have a shrinkwrap
+    if (await fs.exists(path.join(this.config.cwd, 'npm-shrinkwrap.json'))) {
+      this.reporter.error(this.reporter.lang('shrinkwrapWarning'));
+    }
+
     //
     let patterns = rawPatterns;
     let steps: Array<(curr: number, total: number) => Promise<void>> = [];

src/reporters/lang/en.js

@@ -51,6 +51,7 @@ let messages = {
   invalidHostedGitFragment: 'Invalid hosted git fragment $0.',
   couldntFindManifestIn: "Couldn't find manifest in $0.",
   invalidFragment: 'Invalid fragment $0.',
+  shrinkwrapWarning: 'npm-shrinkwrap.json found. This will not be updated or respected. See [TODO] for more information.',
 
   commandNotSpecified: 'No command specified.',
   possibleCommands: 'Possible commands',