Installation failed: Package zlib was not found in the pkg-config search path

I'm trying to install canvas on macOS Mojave 10.14.5. I executed `brew install pkg-config cairo pango libpng jpeg giflib librsvg` but there is still an error.

## Issue or Feature
When i type `npm i canvas` the following log appears:
```
MACBOOK:project user$ npm i canvas

> canvas@2.6.0 install /Users/user/Desktop/project/node_modules/canvas
> node-pre-gyp install --fallback-to-build

node-pre-gyp WARN Using request for node-pre-gyp https download
node-pre-gyp WARN Pre-built binaries not installable for canvas@2.6.0 and node@10.15.3 (node-v64 ABI, unknown) (falling back to source compile with node-gyp)
node-pre-gyp WARN Hit error unable to get local issuer certificate
Package zlib was not found in the pkg-config search path.
Perhaps you should add the directory containing `zlib.pc'
to the PKG_CONFIG_PATH environment variable
Package 'zlib', required by 'libpng', not found
gyp: Call to 'pkg-config libpng --libs' returned exit status 1 while in binding.gyp. while trying to load binding.gyp
gyp ERR! configure error
gyp ERR! stack Error: `gyp` failed with exit code: 1
gyp ERR! stack at ChildProcess.onCpExit (/usr/local/lib/node_modules/npm/node_modules/node-gyp/lib/configure.js:345:16)
gyp ERR! stack at ChildProcess.emit (events.js:189:13)
gyp ERR! stack at Process.ChildProcess._handle.onexit (internal/child_process.js:248:12)
gyp ERR! System Darwin 18.6.0
gyp ERR! command "/usr/local/bin/node" "/usr/local/lib/node_modules/npm/node_modules/node-gyp/bin/node-gyp.js" "configure" "--fallback-to-build" "--module=/Users/user/Desktop/project/node_modules/canvas/build/Release/canvas.node" "--module_name=canvas" "--module_path=/Users/user/Desktop/project/node_modules/canvas/build/Release" "--napi_version=3" "--node_abi_napi=napi" "--napi_build_version=0" "--node_napi_label=node-v64" "--python=/usr/bin/python"
gyp ERR! cwd /Users/user/Desktop/project/node_modules/canvas
gyp ERR! node -v v10.15.3
gyp ERR! node-gyp -v v3.8.0
gyp ERR! not ok
node-pre-gyp ERR! build error
node-pre-gyp ERR! stack Error: Failed to execute '/usr/local/bin/node /usr/local/lib/node_modules/npm/node_modules/node-gyp/bin/node-gyp.js configure --fallback-to-build --module=/Users/user/Desktop/project/node_modules/canvas/build/Release/canvas.node --module_name=canvas --module_path=/Users/user/Desktop/project/node_modules/canvas/build/Release --napi_version=3 --node_abi_napi=napi --napi_build_version=0 --node_napi_label=node-v64 --python=/usr/bin/python' (1)
node-pre-gyp ERR! stack at ChildProcess. (/Users/user/Desktop/project/node_modules/node-pre-gyp/lib/util/compile.js:83:29)
node-pre-gyp ERR! stack at ChildProcess.emit (events.js:189:13)
node-pre-gyp ERR! stack at maybeClose (internal/child_process.js:970:16)
node-pre-gyp ERR! stack at Process.ChildProcess._handle.onexit (internal/child_process.js:259:5)
node-pre-gyp ERR! System Darwin 18.6.0
node-pre-gyp ERR! command "/usr/local/bin/node" "/Users/user/Desktop/project/node_modules/.bin/node-pre-gyp" "install" "--fallback-to-build"
node-pre-gyp ERR! cwd /Users/user/Desktop/project/node_modules/canvas
node-pre-gyp ERR! node -v v10.15.3
node-pre-gyp ERR! node-pre-gyp -v v0.11.0
node-pre-gyp ERR! not ok
Failed to execute '/usr/local/bin/node /usr/local/lib/node_modules/npm/node_modules/node-gyp/bin/node-gyp.js configure --fallback-to-build --module=/Users/user/Desktop/project/node_modules/canvas/build/Release/canvas.node --module_name=canvas --module_path=/Users/user/Desktop/project/node_modules/canvas/build/Release --napi_version=3 --node_abi_napi=napi --napi_build_version=0 --node_napi_label=node-v64 --python=/usr/bin/python' (1)
npm WARN project@0.3.0 No license field.

npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! canvas@2.6.0 install: `node-pre-gyp install --fallback-to-build`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the canvas@2.6.0 install script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR! /Users/user/.npm/_logs/2019-11-14T12_32_18_808Z-debug.log

```

## Your Environment
* Version of node-canvas: 2.6.0
* Environment: npm 6.4.1 with node 10.15.3 on macOS Mojave 10.14.5