feat: release Dashboard 2.15.1 (#444)

diff --git a/.github/workflows/dashboard_all_in_one_ci.yaml b/.github/workflows/dashboard_all_in_one_ci.yaml
index 5d5163a..176d058 100644
--- a/.github/workflows/dashboard_all_in_one_ci.yaml
+++ b/.github/workflows/dashboard_all_in_one_ci.yaml
@@ -13,7 +13,7 @@
     runs-on: ubuntu-latest
 
     env:
-      APISIX_DASHBOARD_VERSION: "3.0.0" # in semver
+      APISIX_DASHBOARD_VERSION: "2.15.1" # in semver
     
     steps:
       - uses: actions/checkout@v2
diff --git a/.github/workflows/dashboard_push_docker_hub.yaml b/.github/workflows/dashboard_push_docker_hub.yaml
index 88a7e5a..f22c56e 100644
--- a/.github/workflows/dashboard_push_docker_hub.yaml
+++ b/.github/workflows/dashboard_push_docker_hub.yaml
@@ -15,7 +15,7 @@
     runs-on: ubuntu-latest
 
     env:
-      APISIX_DASHBOARD_VERSION: "3.0.0" # in semver
+      APISIX_DASHBOARD_VERSION: "2.15.1" # in semver
 
     steps:
       - name: Check out the repo
diff --git a/Makefile b/Makefile
index c2fd8d0..fcf835d 100644
--- a/Makefile
+++ b/Makefile
@@ -26,7 +26,7 @@
 IMAGE_NAME = apache/apisix
 IMAGE_TAR_NAME = apache_apisix
 
-APISIX_DASHBOARD_VERSION ?= $(shell echo ${APISIX_DASHBOARD_VERSION:=3.0.0})
+APISIX_DASHBOARD_VERSION ?= $(shell echo ${APISIX_DASHBOARD_VERSION:=2.15.1})
 APISIX_DASHBOARD_IMAGE_NAME = apache/apisix-dashboard
 APISIX_DASHBOARD_IMAGE_TAR_NAME = apache_apisix_dashboard