Add missing space in algorithm step.

index.html

@@ -1915,7 +1915,7 @@ <h3>Add Proof Set/Chain</h3>
           <li>
 If |options| has a `previousProof` [=struct/item=] that is a string, add the
 element from |allProofs| with an `id` attribute matching `previousProof` to
-|matchingProofs|. If a proof with `id` equal to `previousProof`does not exist in
+|matchingProofs|. If a proof with `id` equal to `previousProof` does not exist in
 |allProofs|, an error MUST be raised and SHOULD convey an error type of
 <a href="#PROOF_GENERATION_ERROR">PROOF_GENERATION_ERROR</a>.
           </li>