_content/doc: always update install tab version numbers

Fixes golang/go#69603

Change-Id: I5dd8910dd7a6f9c758a8f755eeb544d2d95446dc
Reviewed-on: https://go-review.googlesource.com/c/website/+/620556
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Matloob <matloob@golang.org>

_content/doc/download.js

diff --git a/_content/doc/download.js b/_content/doc/download.js
index ef9efb4..9f2f9e0 100644
--- a/_content/doc/download.js
+++ b/_content/doc/download.js
@@ -24,12 +24,15 @@
             this.linuxFileName = file;
           }
         }
+
+        this.setVersion(data[0].version);
+        this.tabs.forEach(el => this.setInstallTabData(el.id));
+
         this.detectOS();
         const osTab = document.getElementById(this.osName);
         if (osTab !== null) {
           osTab.click();
         }
-        this.setVersion(data[0].version);
       })
       .catch(console.error);
       this.setEventListeners();
@@ -70,8 +73,6 @@
       this.osName = 'linux';
     } else if (navigator.userAgent.indexOf('Mac') !== -1) {
       this.osName = 'mac';
-    } else if (navigator.userAgent.indexOf('X11') !== -1) {
-      this.osName = 'unix';
     } else if (navigator.userAgent.indexOf('Win') !== -1) {
       this.osName = 'windows';
     }
@@ -93,7 +94,6 @@
   handleTabClick(e) {
     const el = (e.target);
     this.activateTab(Array.prototype.indexOf.call(this.tabs, el));
-    this.setInstallTabData(el.id);
   }
 
   // get version number.