Apply style suggestions from code review

Author: andrjohns

stan/math/fwd/fun/sqrt.hpp

@@ -16,8 +16,9 @@ namespace math {
 template <typename T>
 inline fvar<T> sqrt(const fvar<T>& x) {
   using std::sqrt;
-  if (value_of_rec(x.val_) == 0.0)
+  if (value_of_rec(x.val_) == 0.0) {
     return fvar<T>(sqrt(x.val_), 0.0 * x.d_);
+  }
   return fvar<T>(sqrt(x.val_), 0.5 * x.d_ * inv_sqrt(x.val_));
 }
 

stan/math/rev/fun/sqrt.hpp

@@ -43,8 +43,9 @@ namespace math {
  */
 inline var sqrt(const var& a) {
   return make_callback_var(std::sqrt(a.val()), [a](auto& vi) mutable {
-    if (vi.val() != 0.0)
+    if (vi.val() != 0.0) {
       a.adj() += vi.adj() / (2.0 * vi.val());
+    }
   });
 }