feat: Update promptfoo eval command in Makefile

This commit updates the promptfoo eval command in the Makefile to include the option to specify the name of the eval directory. This allows for more flexibility when running evaluations.

test/evals/promptfoo-poc/README.md

@@ -20,7 +20,7 @@ To run or create evals, you will need to have the following installed:
 To run the evaluations, you can cd into the relevant directory and use the following command:
 
 ```bash
-make evals
+make eval <name_of_eval_dir>
 ```
 
 Or, you can run all the evaluations by running the following command:

test/evals/promptfoo-poc/fix/fix.prompt.txt

@@ -84,12 +84,12 @@ You MUST ensure the line numbers for the 'old' property correctly remove *ALL* c
   Example change object:
   ---
   {
-    summary: "Fix syntax error in loop body.",
-    old: {
-      startLineString: "pdx-5: for i := 0; i < 10; i++ { ",
-      endLineString: "pdx-7: }",
+    "summary": "Fix syntax error in loop body.",
+   	"old": {
+      "startLineString": "pdx-5: for i := 0; i < 10; i++ { ",
+      "endLineString": "pdx-7: }"
     },
-    new: "for i := 0; i < 10; i++ {\n  execQuery()\n  }\n  }\n}",
+    "new": "for i := 0; i < 10; i++ {\n  execQuery()\n  }\n  }\n}"
   }
   ---