add dimensions missing parameter to vector

Author: wilsenhc

migrations.md

@@ -924,7 +924,7 @@ The `uuid` method creates a `UUID` equivalent column:
 
 The `vector` method creates a `vector` equivalent column:
 
-    $table->vector('embedding');
+    $table->vector('embedding', dimensions: 100);
 
 <a name="column-method-year"></a>
 #### `year()` {.collection-method}