Remove trailing "=" from JS version of sha256_b64

src/platform/js/platform.ml

@@ -30,8 +30,13 @@ let sha256_hex x =
     [| sha256 x |] |> Js.to_string
 
 let sha256_b64 x =
-  Js.Unsafe.meth_call sjcl "codec.base64.fromBits"
-    [| sha256 x |] |> Js.to_string
+  let raw =
+    Js.Unsafe.meth_call sjcl "codec.base64.fromBits"
+      [| sha256 x |] |> Js.to_string
+  in
+  match (try Some (String.index raw '=') with Not_found -> None) with
+  | Some i -> String.sub raw 0 i
+  | None -> raw
 
 let b64_encode_compact x = assert false