Fix false "subject not capitalized" errors (fixes #1)

Fix bug that on some environments caused valid commit messages being
reported as having a non-capitalized subject line. For example, subject
line such as "Version bump 1.0.0" was reported as not being capitalized
because the regular expression used a character range [a-z] that on
some systems is interpreted as containing uppercase characters as well
(depends on LC_COLLATE environment variable).

lint-commit-msg

@@ -496,7 +496,7 @@ while true; do
         # errors that only confuse the user.
 
         # Capitalization check
-        [[ ${subject} =~ ^[a-z] ]] &&
+        [[ ${subject} =~ ^[[:lower:]] ]] &&
             append_error \
                 "${error_subject_not_capitalized}" \
                 "subject${LCM_SUBJECT_LINE_PREFIX_REGEX:+ \"${subject}\"} not capitalized" \