Update API Pagination response headers

Reflecting that they now return lower case responses.

doc/api/README.md

@@ -374,22 +374,22 @@ curl --head --header "PRIVATE-TOKEN: <your_access_token>" "https://gitlab.exampl
 The response will then be:
 
 ```http
-HTTP/1.1 200 OK
-Cache-Control: no-cache
-Content-Length: 1103
-Content-Type: application/json
-Date: Mon, 18 Jan 2016 09:43:18 GMT
-Link: <https://gitlab.example.com/api/v4/projects/8/issues/8/notes?page=1&per_page=3>; rel="prev", <https://gitlab.example.com/api/v4/projects/8/issues/8/notes?page=3&per_page=3>; rel="next", <https://gitlab.example.com/api/v4/projects/8/issues/8/notes?page=1&per_page=3>; rel="first", <https://gitlab.example.com/api/v4/projects/8/issues/8/notes?page=3&per_page=3>; rel="last"
-Status: 200 OK
-Vary: Origin
-X-Next-Page: 3
-X-Page: 2
-X-Per-Page: 3
-X-Prev-Page: 1
-X-Request-Id: 732ad4ee-9870-4866-a199-a9db0cde3c86
-X-Runtime: 0.108688
-X-Total: 8
-X-Total-Pages: 3
+HTTP/2 200 OK
+cache-control: no-cache
+content-length: 1103
+content-type: application/json
+date: Mon, 18 Jan 2016 09:43:18 GMT
+link: <https://gitlab.example.com/api/v4/projects/8/issues/8/notes?page=1&per_page=3>; rel="prev", <https://gitlab.example.com/api/v4/projects/8/issues/8/notes?page=3&per_page=3>; rel="next", <https://gitlab.example.com/api/v4/projects/8/issues/8/notes?page=1&per_page=3>; rel="first", <https://gitlab.example.com/api/v4/projects/8/issues/8/notes?page=3&per_page=3>; rel="last"
+status: 200 OK
+vary: Origin
+x-next-page: 3
+x-page: 2
+x-per-page: 3
+x-prev-page: 1
+x-request-id: 732ad4ee-9870-4866-a199-a9db0cde3c86
+x-runtime: 0.108688
+x-total: 8
+x-total-pages: 3
 ```
 
 #### Other pagination headers
@@ -398,12 +398,12 @@ GitLab also returns the following additional pagination headers:
 
 | Header          | Description                                   |
 | --------------- | --------------------------------------------- |
-| `X-Total`       | The total number of items                     |
-| `X-Total-Pages` | The total number of pages                     |
-| `X-Per-Page`    | The number of items per page                  |
-| `X-Page`        | The index of the current page (starting at 1) |
-| `X-Next-Page`   | The index of the next page                    |
-| `X-Prev-Page`   | The index of the previous page                |
+| `x-total`       | The total number of items                     |
+| `x-total-pages` | The total number of pages                     |
+| `x-per-page`    | The number of items per page                  |
+| `x-page`        | The index of the current page (starting at 1) |
+| `x-next-page`   | The index of the next page                    |
+| `X-prev-page`   | The index of the previous page                |
 
 NOTE: **Note:**
 For GitLab.com users, [some pagination headers may not be returned](../user/gitlab_com/index.md#pagination-response-headers).

doc/user/gitlab_com/index.md

@@ -541,9 +541,9 @@ Source:
 For performance reasons, if a query returns more than 10,000 records, GitLab
 doesn't return the following headers:
 
-- `X-Total`.
-- `X-Total-Pages`.
-- `rel="last"` `Link`.
+- `x-total`.
+- `x-total-pages`.
+- `rel="last"` `link`.
 
 ### Rack Attack initializer