Fix shellcheck warnings for bootstrap-osx-homebrew.sh (#1058)

Summary:
- Fix a few shellcheck warnings on `bootstrap-osx-homebrew.sh`.
- This will help when new changes are made to this script as
  shellcheck is run internally.
Pull Request resolved: https://github.com/facebook/folly/pull/1058

Differential Revision: D14493361

Pulled By: yfeldblum

fbshipit-source-id: e46f9d0e329fd1ebe16820bdb5614c53363c5dfe

folly/build/bootstrap-osx-homebrew.sh

@@ -10,7 +10,7 @@ cd "$BASE_DIR"
 
 # brew install alias
 brew_install() {
-    brew install $@ || brew upgrade $@
+    brew install "$@" || brew upgrade "$@"
 }
 
 # install deps
@@ -19,8 +19,8 @@ install_deps() {
 	dependencies=(autoconf automake libtool pkg-config double-conversion glog gflags boost libevent xz snappy lz4 jemalloc openssl)
 
 	# fetch deps
-	for dependency in ${dependencies[@]}; do
-		brew_install ${dependency}
+	for dependency in "${dependencies[@]}"; do
+		brew_install "${dependency}"
 	done
 }