Fix clippy warnings

error: use of `.unwrap_or_else(..)` to construct default value
  --> src/http.rs:73:16
   |
73 |     let resp = get_html_section(&resp, "main").unwrap_or_else(|| "".to_string());
   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `get_html_section(&resp, "main").unwrap_or_default()`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unwrap_or_else_default

error: use of `.unwrap_or_else(..)` to construct default value
  --> src/http.rs:37:17
   |
37 |     let brief = get_html_section(&brief, "main").unwrap_or_else(|| "".to_string());
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `get_html_section(&brief, "main").unwrap_or_default()`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unwrap_or_else_default
   = note: `-D clippy::unwrap-or-else-default` implied by `-D warnings`

src/http.rs

@@ -34,7 +34,7 @@ fn get_content(aoc: &Aoc, suffix: &str) -> Result<String, Error> {
 pub fn get_brief(aoc: &Aoc) -> Result<(String, String), Error> {
     let brief = get_content(aoc, "")?;
     let title = get_title(&brief).unwrap_or_default();
-    let brief = get_html_section(&brief, "main").unwrap_or_else(|| "".to_string());
+    let brief = get_html_section(&brief, "main").unwrap_or_default();
     let brief = parse_html(&brief);
     let num_lines = brief.lines().count();
     let brief = brief.lines()
@@ -70,7 +70,7 @@ pub fn submit(aoc: &Aoc, solution: &str) -> Result<String, Error> {
         ])?
         .into_string()?;
 
-    let resp = get_html_section(&resp, "main").unwrap_or_else(|| "".to_string());
+    let resp = get_html_section(&resp, "main").unwrap_or_default();
     let resp = parse_html(&resp);
     let resp = resp.trim().to_string();
     Ok(resp)