Added build flags for iconv in osx build

Author: Nick-S-2018

build-osx

@@ -95,7 +95,7 @@ chmod +x configure
   --with-rdkafka \
 	--enable-jchash \
 	--enable-simdjson \
-  --with-openssl --with-zlib --with-zip --with-iconv \
+  --with-openssl --with-zlib --with-zip --with-iconv=$(brew --prefix libiconv) \
   --enable-filter \
   --with-curl \
   --enable-opcache \