cargo test --doc failed on Alpine distribution

[jcamiel]

Summary

cargo test --doc is failing on Alpine

/home/hurl # cargo test --doc
    Finished test [unoptimized + debuginfo] target(s) in 0.08s
   Doc-tests hurl

running 3 tests
test src/html/escape.rs - html::escape::html_escape (line 26) ... FAILED
test src/html/unescape.rs - html::unescape::html_unescape (line 104) ... FAILED
test src/runner/hurl_file.rs - runner::hurl_file::run (line 41) ... FAILED

failures:

---- src/html/escape.rs - html::escape::html_escape (line 26) stdout ----
Couldn't run the test: No such file or directory (os error 2)
---- src/html/unescape.rs - html::unescape::html_unescape (line 104) stdout ----
Couldn't run the test: No such file or directory (os error 2)
---- src/runner/hurl_file.rs - runner::hurl_file::run (line 41) stdout ----
Couldn't run the test: No such file or directory (os error 2)

failures:
    src/html/escape.rs - html::escape::html_escape (line 26)
    src/html/unescape.rs - html::unescape::html_unescape (line 104)
    src/runner/hurl_file.rs - runner::hurl_file::run (line 41)

test result: FAILED. 0 passed; 3 failed; 0 ignored; 0 measured; 0 filtered out; finished in 3.89s

This is blocking #1122

Tested on Alpine Docker image