Update Evergreen config to test against PHPC master branch

Author: jmikola

.evergreen/config.yml

@@ -621,22 +621,22 @@ axes:
   - id: driver-versions
     display_name: Driver Version
     values:
-      # TODO: Update to "1.14.0" once PHPC 1.14.0 is released
+      # TODO: Update to "1.15.0" once PHPC 1.15.0 is released
       - id: "oldest-supported"
-        # display_name: "1.14.0"
-        display_name: "PHPC 1.14-dev (master)"
+        # display_name: "1.15.0"
+        display_name: "PHPC 1.15-dev (master)"
         variables:
-          # EXTENSION_VERSION: "1.14.0"
+          # EXTENSION_VERSION: "1.15.0"
           EXTENSION_BRANCH: "master"
-      # TODO: Update to "1.14.x"/"stable" once PHPC 1.14.0 is released
+      # TODO: Update to "1.15.x"/"stable" once PHPC 1.15.0 is released
       - id: "latest-stable"
-        # display_name: "1.14.x"
-        display_name: "PHPC 1.14-dev (master)"
+        # display_name: "1.15.x"
+        display_name: "PHPC 1.15-dev (master)"
         variables:
           # EXTENSION_VERSION: "stable"
           EXTENSION_BRANCH: "master"
       - id: "latest-dev"
-        display_name: "PHPC 1.14-dev (master)"
+        display_name: "PHPC 1.15-dev (master)"
         variables:
           EXTENSION_BRANCH: "master"