[fixup] isForkEnabled

[ch4ot1c]

dsktp@dsktp-VirtualBox:~/BTCP-Rebase$ make
Making all in src
make[1]: Entering directory '/home/dsktp/BTCP-Rebase/src'
make[2]: Entering directory '/home/dsktp/BTCP-Rebase/src'
make[3]: Entering directory '/home/dsktp/BTCP-Rebase'
make[3]: Leaving directory '/home/dsktp/BTCP-Rebase'
make[3]: Entering directory '/home/dsktp/BTCP-Rebase/src/secp256k1'
make[3]: Leaving directory '/home/dsktp/BTCP-Rebase/src/secp256k1'
  CXX      libbitcoin_server_a-validation.o
validation.cpp: In function ‘CAmount GetBlockSubsidy(int, const Consensus::Params&)’:
validation.cpp:1193:29: error: too few arguments to function ‘bool isForkEnabled(int, int)’
     if(isForkEnabled(nHeight)) {
                             ^
In file included from validation.cpp:18:0:
./fork.h:24:13: note: declared here
 inline bool isForkEnabled(int nHeight, int forkStartHeight)
             ^~~~~~~~~~~~~
validation.cpp:1198:29: error: too few arguments to function ‘bool isForkEnabled(int, int)’
     if(isForkEnabled(nHeight))
                             ^
In file included from validation.cpp:18:0:
./fork.h:24:13: note: declared here
 inline bool isForkEnabled(int nHeight, int forkStartHeight)
             ^~~~~~~~~~~~~
Makefile:6492: recipe for target 'libbitcoin_server_a-validation.o' failed

Please test + be cautious when merging pull requests:

The Linux build needs to never break, enforced by GH / Travis CI (Shoutout #19)