Replace "unspecified" with "not specified"

Co-authored-by: Vadim Petrochenkov <[email protected]>

Author: ShE3py

compiler/rustc_session/src/options.rs

@@ -1838,7 +1838,7 @@ written to standard error output)"),
     trap_unreachable: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "generate trap instructions for unreachable intrinsics (default: use target setting, usually yes)"),
     treat_err_as_bug: Option<NonZeroUsize> = (None, parse_treat_err_as_bug, [TRACKED],
-        "treat the `val`th error that occurs as bug (default if unspecified: 0 - don't treat errors as bugs. \
+        "treat the `val`th error that occurs as bug (default if not specified: 0 - don't treat errors as bugs. \
         default if specified without a value: 1 - treat the first error as bug)"),
     trim_diagnostic_paths: bool = (true, parse_bool, [UNTRACKED],
         "in diagnostics, use heuristics to shorten paths referring to items"),