Fix newer GCC compile errors

[atyndall]

In newer versions of GCC, compiling this gem fails with errors like;

Building native extensions. This could take a while...
ERROR:  Error installing cld2-1.0.3.gem:
  ERROR: Failed to build gem native extension.

    current directory: /var/lib/gems/2.5.0/gems/cld2-1.0.3/ext/cld
/usr/bin/ruby2.5 -r ./siteconf20180907-25240-hhk5um.rb extconf.rb
checking for -lstdc++... yes
creating Makefile

current directory: /var/lib/gems/2.5.0/gems/cld2-1.0.3/ext/cld
make "DESTDIR=" clean

current directory: /var/lib/gems/2.5.0/gems/cld2-1.0.3/ext/cld
make "DESTDIR="
compiling internal/cld2_generated_cjk_compatible.cc
compiling internal/cld2_generated_deltaoctachrome0122.cc
compiling internal/cld2_generated_distinctoctachrome0122.cc
compiling internal/cld2_generated_quadchrome0122_2.cc
compiling internal/cld_generated_cjk_delta_bi_4.cc
compiling internal/cld_generated_cjk_uni_prop_80.cc
internal/cld_generated_cjk_uni_prop_80.cc:7089:1: error: narrowing conversion of ‘-14’ from ‘int’ to ‘CLD2::uint8 {aka unsigned char}’ inside { } [-Wnarrowing]
 };
 ^
internal/cld_generated_cjk_uni_prop_80.cc:7089:1: error: narrowing conversion of ‘-14’ from ‘int’ to ‘CLD2::uint8 {aka unsigned char}’ inside { } [-Wnarrowing]
internal/cld_generated_cjk_uni_prop_80.cc:7089:1: error: narrowing conversion of ‘-14’ from ‘int’ to ‘CLD2::uint8 {aka unsigned char}’ inside { } [-Wnarrowing]
[omitted]
Makefile:210: recipe for target 'internal/cld_generated_cjk_uni_prop_80.o' failed
make: *** [internal/cld_generated_cjk_uni_prop_80.o] Error 1

make failed, exit code 2

Gem files will remain installed in /var/lib/gems/2.5.0/gems/cld2-1.0.3 for inspection.
Results logged to /var/lib/gems/2.5.0/extensions/x86_64-linux/2.5.0/cld2-1.0.3/gem_make.out

As per the recommendation in CLD2Owners/cld2#47 (comment) I have added the necessary flag to prevent these errors. The gem now compiles for me on Ubuntu 18.04 with gcc 7.3.0.

[craig-day]

@alessandrobanjo (does that user even exist anymore?)

[craig-day]

@codenothing @girak @Wolfcrush can someone merge this and release a new gem version?

[mariozaizar]

+1