pack OPENSCAD_NOGUI in qmake nogui config

thus, scintilla can be kept from being built at all, slimming down the
build dependencies for the nogui build

openscad.pro

@@ -208,13 +208,19 @@ CONFIG += fontconfig
 CONFIG += gettext
 
 #Uncomment the following line to enable the QScintilla editor
-CONFIG += scintilla
+!nogui {
+  CONFIG += scintilla
+}
 
 # Make experimental features available
 experimental {
   DEFINES += ENABLE_EXPERIMENTAL
 }
 
+nogui {
+  DEFINES += OPENSCAD_NOGUI
+}
+
 mdi {
   DEFINES += ENABLE_MDI
 }

scripts/travis-ci.sh

@@ -1,6 +1,6 @@
 #!/bin/bash
 
-qmake CONFIG+=experimental DEFINES+=OPENSCAD_NOGUI
+qmake CONFIG+=experimental CONFIG+=nogui
 make
 
 cd tests