Correct typo in test descriptions

.../language/expressions/compound-assignment/11.13.2-45-s.js

.../language/expressions/compound-assignment/11.13.2-46-s.js

.../language/expressions/compound-assignment/11.13.2-47-s.js

.../language/expressions/compound-assignment/11.13.2-48-s.js

.../language/expressions/compound-assignment/11.13.2-49-s.js

.../language/expressions/compound-assignment/11.13.2-50-s.js

.../language/expressions/compound-assignment/11.13.2-51-s.js

.../language/expressions/compound-assignment/11.13.2-53-s.js

.../language/expressions/compound-assignment/11.13.2-54-s.js

.../language/expressions/compound-assignment/11.13.2-55-s.js