Fix Travis-build Recipe

Swap tabs to spaces, and use gpiozero.tools.negated

docs/recipes.rst

@@ -196,7 +196,7 @@ Button controlled camera
 ========================
 
 Using the button press to trigger picamera to take a pitcure using
-``button.when_pressed = camera.capture`` would not work because it requires an
+``button/when_pressed = camera.capture`` would not work because it requires an
 ``output`` parameter. However, this can be achieved using a custom function
 which requires no parameters::
     
@@ -328,6 +328,7 @@ tests are passing, a red light means the build is broken::
 
     from travispy import TravisPy
     from gpiozero import LED
+    from gpiozero.tools import negated
     from time import sleep
     from signal import pause
 
@@ -338,14 +339,10 @@ tests are passing, a red light means the build is broken::
             yield r.last_build_state == 'passed'
             sleep(delay) # Sleep an hour before hitting travis again
 
-	def invert(values):
-		for value in values:
-			yield not value
-
     red = LED(12)
     green = LED(16)
 
-	red.source = invert(green.values)
+    red.source = negated(green.values)
     green.source = build_passed()
     pause()