remove // support, as it never worked

if you want to escape a /, do it with \/ or just precede with a space

src/SlashCommands.js

@@ -434,7 +434,7 @@ module.exports = {
         // trim any trailing whitespace, as it can confuse the parser for
         // IRC-style commands
         input = input.replace(/\s+$/, "");
-        if (input[0] === "/" && input[1] !== "/") {
+        if (input[0] === "/") {
             const bits = input.match(/^(\S+?)( +((.|\n)*))?$/);
             let cmd;
             let args;

src/components/views/rooms/MessageComposerInput.js

@@ -731,7 +731,7 @@ export default class MessageComposerInput extends React.Component {
         const firstGrandChild = firstChild && firstChild.nodes.get(0);
         if (firstChild && firstGrandChild &&
             firstChild.object === 'block' && firstGrandChild.object === 'text' &&
-            firstGrandChild.text[0] === '/' && firstGrandChild.text[1] !== '/')
+            firstGrandChild.text[0] === '/')
         {
             commandText = this.plainWithIdPills.serialize(editorState);
             cmd = SlashCommands.processInput(this.props.room.roomId, commandText);