Fix label not starting with lcase-letter

Co-authored-by: Fridtjof Stoldt <xFrednet@gmail.com>

Author: lukaslueg

clippy_lints/src/if_let_mutex.rs

@@ -64,7 +64,7 @@ impl<'tcx> LateLintPass<'tcx> for IfLetMutex {
  let diag = |diag: &mut Diagnostic| {
  diag.span_label(
  op_mutex.span,
- "This Mutex will remain locked for the entire `if let`-block...",
+ "this Mutex will remain locked for the entire `if let`-block...",
  );
  diag.span_label(
  arm_mutex.span,

tests/ui/if_let_mutex.stderr

@@ -2,7 +2,7 @@ error: calling `Mutex::lock` inside the scope of another `Mutex::lock` causes a
  --> $DIR/if_let_mutex.rs:10:5
  |
 LL | if let Err(locked) = m.lock() {
- | ^ - This Mutex will remain locked for the entire `if let`-block...
+ | ^ - this Mutex will remain locked for the entire `if let`-block...
  | _____|
  | |
 LL | | do_stuff(locked);
@@ -20,7 +20,7 @@ error: calling `Mutex::lock` inside the scope of another `Mutex::lock` causes a
  --> $DIR/if_let_mutex.rs:22:5
  |
 LL | if let Some(locked) = m.lock().unwrap().deref() {
- | ^ - This Mutex will remain locked for the entire `if let`-block...
+ | ^ - this Mutex will remain locked for the entire `if let`-block...
  | _____|
  | |
 LL | | do_stuff(locked);
@@ -37,7 +37,7 @@ error: calling `Mutex::lock` inside the scope of another `Mutex::lock` causes a
  --> $DIR/if_let_mutex.rs:43:5
  |
 LL | if let Ok(i) = mutex.lock() {
- | ^ ----- This Mutex will remain locked for the entire `if let`-block...
+ | ^ ----- this Mutex will remain locked for the entire `if let`-block...
  | _____|
  | |
 LL | | do_stuff(i);