fix(bash): Silently fail if pkg-config bash-completion exists with non 0

Meaning bash-completion is either not installed or misconfigured with
PKG_CONFIG_PATH. It'll fallback to only two possible installation, stdout and
~/.bashrc

lib/installer.js

@@ -245,7 +245,12 @@ export default class Installer {
       var cmd = `pkg-config --variable=${variable} bash-completion`;
       debug('cmd', cmd);
       exec(cmd, function(err, stdout, stderr) {
-        if (err) return errback(err);
+        if (err) {
+          // silently fail if pkg-config bash-completion returns an error,
+          // meaning bash-completion is either not installed or misconfigured
+          // with PKG_CONFIG_PATH
+          return r();
+        }
         stdout = stdout.trim();
         debug('Got %s for %s', stdout, variable);
         r(stdout);