It should be "the resulting cache key", not "the resulting `cache-key`" [ci skip]

This is a partial revert of 07402aa1307a4ff71b4ef6581f95b8612238a6af.

I also changed "cache-key" to "cache key" because "cache-key" appears
only once in the repo.

```
% git grep '\bcache-key\b' | wc -l
1

% git grep '\bcache key\b' | wc -l
28
```

1 files changed, 1 insertions, 1 deletions

diff --git a/guides/source/caching_with_rails.md b/guides/source/caching_with_rails.md
index cc1e6d92c3..e2ddee3ed5 100644
--- a/guides/source/caching_with_rails.md
+++ b/guides/source/caching_with_rails.md
@@ -284,7 +284,7 @@ class Product < ApplicationRecord
 end
 ```
 
-NOTE: Notice that in this example we used the `cache_key` method, so the resulting `cache-key` will be something like `products/233-20140225082222765838000/competing_price`. `cache_key` generates a string based on the model's `id` and `updated_at` attributes. This is a common convention and has the benefit of invalidating the cache whenever the product is updated. In general, when you use low-level caching for instance level information, you need to generate a cache key.
+NOTE: Notice that in this example we used the `cache_key` method, so the resulting cache key will be something like `products/233-20140225082222765838000/competing_price`. `cache_key` generates a string based on the model's `id` and `updated_at` attributes. This is a common convention and has the benefit of invalidating the cache whenever the product is updated. In general, when you use low-level caching for instance level information, you need to generate a cache key.
 
 ### SQL Caching