Move autojoin zone to us-central1-c (#106)

* Move autojoin zone to us-central1-c

Author: stephen-soltesz

mlab-autojoin/main.tf

@@ -42,5 +42,5 @@ provider "google" {
   alias   = "autojoin"
   project = "mlab-autojoin"
   region  = "us-central1"
-  zone    = "us-central1-a"
+  zone    = "us-central1-c"
 }

mlab-sandbox/main.tf

@@ -42,5 +42,5 @@ provider "google" {
   alias   = "autojoin"
   project = "mlab-sandbox"
   region  = "us-central1"
-  zone    = "us-central1-a"
+  zone    = "us-central1-c"
 }

mlab-staging/main.tf

@@ -42,5 +42,5 @@ provider "google" {
   alias   = "autojoin"
   project = "mlab-staging"
   region  = "us-central1"
-  zone    = "us-central1-a"
+  zone    = "us-central1-c"
 }