couple of trivial fixes to make clippy a bit more happy (#704)

clippy: fix a few lints

The fixes are:

  * Use single quotes for single-character
  * Use ticks in documentation when necessary.
  * Just bow to clippy's wisdom.

tests/tests.rs

@@ -62,7 +62,7 @@ fn paths(unix: &[&str]) -> Vec<String> {
 
 fn paths_from_stdout(stdout: String) -> Vec<String> {
     let mut paths: Vec<_> = stdout.lines().map(|s| {
-        s.split(":").next().unwrap().to_string()
+        s.split(':').next().unwrap().to_string()
     }).collect();
     paths.sort();
     paths

tests/workdir.rs

@@ -13,7 +13,7 @@ use std::time::Duration;
 static TEST_DIR: &'static str = "ripgrep-tests";
 static NEXT_ID: AtomicUsize = ATOMIC_USIZE_INIT;
 
-/// WorkDir represents a directory in which tests are run.
+/// `WorkDir` represents a directory in which tests are run.
 ///
 /// Directories are created from a global atomic counter to avoid duplicates.
 #[derive(Debug)]