feat(install): detect incorrect Go version

lib/install.js

@@ -14,17 +14,27 @@ export default async function installMain(progname, rawArgs, priv) {
     cp.on('exit', resolve);
     cp.on('error', () => resolve(-1));
   });
-
+
+  const spawnOutput = (cmd, args = [], opts = {}) => new Promise((resolve, reject) => {
+    let buf = '';
+    const cp = spawn(cmd, args, { ...opts, stdio: ['inherit', 'pipe', 'inherit' ] });
+    cp.stdout.on('data', chunk => buf += String(chunk));
+    cp.on('exit', () => resolve(buf));
+    cp.on('error', () => resolve(buf));
+  });
+
   // Install Yarn.
   const pmRet = await pspawn('yarn', ['--version']);
   if (pmRet !== 0) {
     await pspawn('npm', ['install', '-g', 'yarn'], { stdio: 'inherit' });
   }
   const pm = 'yarn';
 
-  // FIXME: Check for version 1.13.
-  const goRet = await pspawn('go', ['version']);
-  const goCmd = goRet === 0 && pspawn('npm', ['install'], { cwd: '.agservers', stdio: 'inherit' });
+  // Check for golang version 1.12+.
+  const goVsn = await spawnOutput('go', ['version']);
+  const match = goVsn.match(/^go version go1\.(\d+)\./);
+  const goCmd = match && Number(match[1]) >= 12 &&
+    pspawn('npm', ['install'], { cwd: '.agservers', stdio: 'inherit' });
 
   await Promise.all([
     pspawn(pm, ['install'], { cwd: 'ui', stdio: 'inherit' }),
@@ -34,7 +44,7 @@ export default async function installMain(progname, rawArgs, priv) {
   ]);
 
   if (!goCmd) {
-    console.log(chalk.bold.yellow(`To run Agoric locally you will need to install Go and rerun '${progname} install'`));
+    console.log(chalk.bold.yellow(`To run Agoric locally you will need to install Go 1.12+ and rerun '${progname} install'`));
   } else {
     // FIXME: Build the wallet
     await pspawn(pm, ['install'], { cwd: '.agservers/node_modules/@agoric/wallet-frontend' });