Fix typo and align on US spelling

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/scripts/abi_check.py b/scripts/abi_check.py
index 1ef6d66..1f6ac53 100755
--- a/scripts/abi_check.py
+++ b/scripts/abi_check.py
@@ -10,9 +10,9 @@
 
 For the storage format, this script compares the automatically generated
 storage tests and the manual read tests, and complains if there is a
-reduction in coverage. A change in test data will be signalled as a
+reduction in coverage. A change in test data will be signaled as a
 coverage reduction since the old test data is no longer present. A change in
-how test data is presented will be signalled as well; this would be a false
+how test data is presented will be signaled as well; this would be a false
 positive.
 
 The results of the API/ABI comparison are either formatted as HTML and stored
@@ -65,7 +65,7 @@
         configuration.report_dir: directory for output files
         configuration.keep_all_reports: if false, delete old reports
         configuration.brief: if true, output shorter report to stdout
-        configuration.check_api: if true, compare ABIs
+        configuration.check_abi: if true, compare ABIs
         configuration.check_api: if true, compare APIs
         configuration.check_storage: if true, compare storage format tests
         configuration.skip_file: path to file containing symbols and types to skip