style(3p/nix): Add braces around single-line for-loops r/772

These were not caught by the previous clang-tidy invocation, but were
instead sorted out using amber[0] as such:

    ambr --regex 'for (\(.+\))\s([a-z].*;)' 'for $1 { $2 }'

[0]: https://github.com/dalance/amber

1 files changed, 3 insertions, 1 deletions

diff --git a/third_party/nix/src/nix/sigs.cc b/third_party/nix/src/nix/sigs.cc
index d548f5445fe3..0eb16b682973 100644
--- a/third_party/nix/src/nix/sigs.cc
+++ b/third_party/nix/src/nix/sigs.cc
@@ -36,7 +36,9 @@ struct CmdCopySigs : StorePathsCommand {
 
     // FIXME: factor out commonality with MixVerify.
     std::vector<ref<Store>> substituters;
-    for (auto& s : substituterUris) substituters.push_back(openStore(s));
+    for (auto& s : substituterUris) {
+      substituters.push_back(openStore(s));
+    }
 
     ThreadPool pool;