update links to Sourcegraph extensions repo

Author: sqs

src/extension.ts

@@ -54,7 +54,7 @@ export function activate(): void {
                     thread.createdAt
                 )} ago`
 
-            // TODO(slimsag): color scheme detection is impossible, see https://github.com/sourcegraph/sourcegraph-extension-api/issues/63
+            // TODO(slimsag): color scheme detection was impossible when this was written, see https://github.com/sourcegraph/sourcegraph/issues/732
             const color = (global as any).location.host === 'github.com' ? 'black' : '#0366d6' // #3b4d6e
             const backgroundColor = (global as any).location.host === 'github.com' ? 'white' : 'rgba(28, 126, 214, 0.3)' // #151c28
 

src/shared/SHARED.md

@@ -1,6 +1,6 @@
 This code is shared between:
 
-- https://github.com/sourcegraph/sourcegraph-extension-api
+- https://docs.sourcegraph.com/extensions
 - https://github.com/sourcegraph/sourcegraph-vscode
 
 Eventually it should be moved into an npm package somewhere. Until then, ensure