build fail with latest pull (new eurorack module)

[davephillips]

Rack 1 dev (from source) Linux Ubuntu 18.04

-g -O3 -march=athlon-fx -funsafe-math-optimizations -Wall -Wextra -Wno-unused-parameter -DARCH_LIN  -c -o build/eurorack/marbles/random/quantizer.cc.o eurorack/marbles/random/quantizer.cc
In file included from ./eurorack/stages/segment_generator.h:36:0,
                 from eurorack/stages/segment_generator.cc:29:
./eurorack/stages/delay_line_16_bits.h:68:10: warning: type qualifiers ignored on function return type [-Wignored-qualifiers]
   inline const float Read(float delay) const {
          ^~~~~
eurorack/stages/segment_generator.cc:53:36: error: ‘kSampleRate’ was not declared in this scope
 const size_t kSampleAndHoldDelay = kSampleRate * 2 / 1000;  // 2 milliseconds
                                    ^~~~~~~~~~~
../../compile.mk:72: recipe for target 'build/eurorack/stages/segment_generator.cc.o' failed
make: *** [build/eurorack/stages/segment_generator.cc.o] Error 1

[AndrewBelt]

Fixed with 7675ebb