docs: fix builder-version swagger

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

api/swagger.yaml

@@ -8023,7 +8023,7 @@ paths:
             API-Version:
               type: "string"
               description: "Max API Version the server supports"
-            BuildKit-Version:
+            Builder-Version:
               type: "string"
               description: "Default version of docker image builder"
             Docker-Experimental:
@@ -8062,7 +8062,7 @@ paths:
             API-Version:
               type: "string"
               description: "Max API Version the server supports"
-            BuildKit-Version:
+            Builder-Version:
               type: "string"
               description: "Default version of docker image builder"
             Docker-Experimental:

docs/api/v1.39.yaml

@@ -7712,7 +7712,7 @@ paths:
             API-Version:
               type: "string"
               description: "Max API Version the server supports"
-            BuildKit-Version:
+            Builder-Version:
               type: "string"
               description: "Default version of docker image builder"
             Docker-Experimental:

docs/api/v1.40.yaml

@@ -7855,7 +7855,7 @@ paths:
             API-Version:
               type: "string"
               description: "Max API Version the server supports"
-            BuildKit-Version:
+            Builder-Version:
               type: "string"
               description: "Default version of docker image builder"
             Docker-Experimental:
@@ -7894,7 +7894,7 @@ paths:
             API-Version:
               type: "string"
               description: "Max API Version the server supports"
-            BuildKit-Version:
+            Builder-Version:
               type: "string"
               description: "Default version of docker image builder"
             Docker-Experimental: