Fix ```mmlu_continuation``` subgroup names to fit Readme and other variants (#3137)

* Update continuation group names to fit Readme

* added changelog to readme and switched datasets form hails to cais

* added missing new line at end of readme

lm_eval/tasks/mmlu/flan_cot_fewshot/_mmlu_flan_cot_fewshot_template_yaml

-dataset_path: hails/mmlu_no_train # a copy of `cais/mmlu` with no auxiliary_train split
+dataset_path: cais/mmlu
 validation_split: validation
 test_split: test
 fewshot_config:

lm_eval/tasks/mmlu/flan_cot_zeroshot/_mmlu_flan_cot_zeroshot_template_yaml

-dataset_path: hails/mmlu_no_train # a copy of `cais/mmlu` with no auxiliary_train split
+dataset_path: cais/mmlu
 validation_split: validation
 fewshot_split: dev
 output_type: generate_until

lm_eval/tasks/mmlu/flan_n_shot/generative/_mmlu_flan_generative_template_yaml

-dataset_path: hails/mmlu_no_train # a copy of `cais/mmlu` with no auxiliary_train split
+dataset_path: cais/mmlu
 test_split: test
 fewshot_split: dev
 fewshot_config:

lm_eval/tasks/mmlu/flan_n_shot/loglikelihood/_mmlu_flan_loglikelihood_template_yaml

-dataset_path: hails/mmlu_no_train # a copy of `cais/mmlu` with no auxiliary_train split
+dataset_path: cais/mmlu
 test_split: test
 fewshot_split: dev
 fewshot_config:

lm_eval/tasks/mmlu/generative/_default_template_yaml

-dataset_path: hails/mmlu_no_train # a copy of `cais/mmlu` with no auxiliary_train split
+dataset_path: cais/mmlu
 test_split: test
 fewshot_split: dev
 fewshot_config: