[setup][osx] Install cmake only if not already installed

setup.sh

@@ -48,7 +48,6 @@ if [ "$(uname)" == "Darwin" ]; then # osx
 
     brew install wget
     brew install coreutils
-    brew install cmake  # should get cmake 3.8
 
 else #linux
     if [[ ! -z "${whoami}" ]]; then #this happens when running in travis
@@ -70,18 +69,25 @@ fi
 
 #download cmake - v3.10.2 is not out of box in Ubuntu 16.04
 if version_less_than_equal_to $cmake_ver $MIN_CMAKE_VERSION; then
-    if [[ ! -d "cmake_build/bin" ]]; then
-        echo "Downloading cmake..."
-        wget https://cmake.org/files/v3.10/cmake-3.10.2.tar.gz \
-            -O cmake.tar.gz
-        tar -xzf cmake.tar.gz
-        rm cmake.tar.gz
-        rm -rf ./cmake_build
-        mv ./cmake-3.10.2 ./cmake_build
-        pushd cmake_build
-        ./bootstrap
-        make
-        popd
+
+    if [ "$(uname)" == "Darwin" ]; then
+        brew install cmake      # should get 3.17 os OSX 10.15
+    else
+
+        if [[ ! -d "cmake_build/bin" ]]; then
+            echo "Downloading cmake..."
+            wget https://cmake.org/files/v3.10/cmake-3.10.2.tar.gz \
+                -O cmake.tar.gz
+            tar -xzf cmake.tar.gz
+            rm cmake.tar.gz
+            rm -rf ./cmake_build
+            mv ./cmake-3.10.2 ./cmake_build
+            pushd cmake_build
+            ./bootstrap
+            make
+            popd
+        fi
+
     fi
 else
     echo "Already have good version of cmake: $cmake_ver"