Rename underscored lifetimes

See https://github.com/rust-lang/rfcs/pull/1177

src/info/filetype.rs

@@ -7,7 +7,7 @@
 use fs::File;
 
 
-impl<'_> File<'_> {
+impl<'a> File<'a> {
 
     /// An “immediate” file is something that can be run or activated somehow
     /// in order to kick off the build of a project. It’s usually only present

src/info/sources.rs

@@ -3,7 +3,7 @@ use std::path::PathBuf;
 use fs::File;
 
 
-impl<'_> File<'_> {
+impl<'a> File<'a> {
 
     /// For this file, return a vector of alternate file paths that, if any of
     /// them exist, mean that *this* file should be coloured as “compiled”.

src/options/filter.rs

@@ -86,8 +86,8 @@ impl FileFilter {
     }
 
     /// Sort the files in the given vector based on the sort field option.
-    pub fn sort_files<'_, F>(&self, files: &mut Vec<F>)
-    where F: AsRef<File<'_>> {
+    pub fn sort_files<'a, F>(&self, files: &mut Vec<F>)
+    where F: AsRef<File<'a>> {
 
         files.sort_by(|a, b| self.compare_files(a.as_ref(), b.as_ref()));