Avoid temporary file for primitive input

This uses primitives new `-o -` option to print the resulting SVG to
stdout. That means we don't need to use a temporary file to capture the
output, which both means one less dependency and running a tad bit
faster. Though to be fair, the run time for primitive dwarfs pretty much
all IO.

fogleman/primitive#71

package.json

@@ -47,7 +47,6 @@
     "fs-extra": "^7.0.1",
     "image-size": "^0.7.1",
     "svgo": "^1.0.5",
-    "tempy": "^0.2.1",
     "yargs": "^11.0.0"
   },
   "repository": {

src/utils/primitive.js

@@ -3,7 +3,6 @@ import os from 'os'
 
 import execa from 'execa'
 import fs from 'fs-extra'
-import tempy from 'tempy'
 
 const VENDOR_DIR = path.resolve(__dirname, '..', '..', 'vendor')
 let primitiveExecutable = 'primitive'
@@ -37,19 +36,18 @@ const checkForPrimitive = async () => {
   }
 }
 
-// Run Primitive with reasonable defaults (rectangles as shapes, 9 shaper per default) to generate the placeholder SVG
+// Run Primitive with reasonable defaults (rectangles as shapes, 9 shaper per
+// default) to generate the placeholder SVG
 const runPrimitive = async (
   filename,
   { numberOfPrimitives = 8, mode = 0 },
   dimensions
 ) => {
-  const primitiveTempFile = tempy.file({ extension: 'svg' })
-
-  await execa(primitiveExecutable, [
+  const { stdout } = await execa(primitiveExecutable, [
     '-i',
     filename,
     '-o',
-    primitiveTempFile,
+    '-',
     '-n',
     numberOfPrimitives,
     '-m',
@@ -58,13 +56,7 @@ const runPrimitive = async (
     findLargerImageDimension(dimensions)
   ])
 
-  const result = await fs.readFile(primitiveTempFile, {
-    encoding: 'utf-8'
-  })
-
-  await fs.unlink(primitiveTempFile)
-
-  return result
+  return stdout
 }
 
 module.exports = {

test/unit/utils/__snapshots__/primitive.test.js.snap

@@ -9,7 +9,7 @@ Array [
     "-i",
     "/path/to/input/file.jpg",
     "-o",
-    "/path/to/output/primitive-tempfile.svg",
+    "-",
     "-n",
     8,
     "-m",
@@ -27,7 +27,7 @@ Array [
     "-i",
     "/path/to/input/file.jpg",
     "-o",
-    "/path/to/output/primitive-tempfile.svg",
+    "-",
     "-n",
     8,
     "-m",
@@ -45,7 +45,7 @@ Array [
     "-i",
     "/path/to/input/file.jpg",
     "-o",
-    "/path/to/output/primitive-tempfile.svg",
+    "-",
     "-n",
     8,
     "-m",