Update install.sh

Added more efficient option to detect number of cores on running system via nproc

install.sh

@@ -47,16 +47,21 @@ function python_finder {
 }
 
 function num_cores {
-  num_cpus=1
-  if [[ `uname -s` == "Linux" ]]; then
-    num_cpus=$(grep -c ^processor /proc/cpuinfo)
+  if [[ -e /bin/nproc ]]; then
+   num_cpus=$(nproc)
   else
-    # Works on Mac and FreeBSD
-    num_cpus=$(sysctl -n hw.ncpu)
+    num_cpus=1
+    if [[ `uname -s` == "Linux" ]]; then
+      num_cpus=$(grep -c ^processor /proc/cpuinfo)
+    else
+      # Works on Mac and FreeBSD
+      num_cpus=$(sysctl -n hw.ncpu)
+    fi
   fi
   echo $num_cpus
 }
 
+
 function install {
   ycm_dir=`pwd`
   build_dir=`mktemp -d -t ycm_build.XXXXXX`