In https://github.com/esp8266/Arduino/pull/4889 the core was modified to

disable WPS by default.  Its only enabled if NO_EXTRA_4K_HEAP is defined.
To enable you must re-run the board manager with --noextra4kheap.
This addes #ifdef NO_EXTRA_4K_HEAP arround WPS usage so it won't generate
compiler errors.

WiFiManager.h

@@ -290,7 +290,9 @@ class WiFiManager
     int            _staShowDns            = 0;     // ternary always show dns, only if not set in code, never(cannot change dns via web!)
     boolean       _removeDuplicateAPs     = true;  // remove dup aps from wifiscan
     boolean       _shouldBreakAfterConfig = false; // stop configportal on save failure
+#ifdef NO_EXTRA_4K_HEAP
     boolean       _tryWPS                 = false; // try WPS on save failure, unsupported
+#endif
     boolean       _configPortalIsBlocking = true;  // configportal enters blocking loop 
     boolean       _enableCaptivePortal    = true;  // enable captive portal redirection
     boolean       _userpersistent         = true;  // users preffered persistence to restore
@@ -316,7 +318,9 @@ class WiFiManager
     void          _end();
 
     void          setupConfigPortal();
+#ifdef NO_EXTRA_4K_HEAP
     void          startWPS();
+#endif
     bool          startAP();
 
     uint8_t       connectWifi(String ssid, String pass);