Travis: try using qpdf appimage to speed up build

.travis.yml

@@ -62,6 +62,12 @@ before_cache:
 before_install: |
   if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then
     bash .travis/linux_before_install.sh
+    pip install --upgrade pip
+    mkdir -p packages /usr/local/bin
+    wget -q 'https://www.dropbox.com/s/vaq0kbwi6e6au80/unpaper_6.1-1.deb?raw=1' -O packages/unpaper_6.1-1.deb
+    sudo dpkg -i packages/unpaper_6.1-1.deb
+    wget -q 'https://github.com/qpdf/qpdf/releases/download/release-qpdf-8.0.2/qpdf-8.0.2-x86_64.AppImage' -O /usr/local/bin/qpdf
+    chmod +x /usr/local/bin/qpdf
   elif [[ "$TRAVIS_OS_NAME" == "osx" ]]; then
     brew update && brew bundle --file=.travis/Brewfile
     pip3 install --upgrade pip

.travis/linux_before_install.sh

@@ -1,21 +0,0 @@
-#!/bin/bash
-# © 2017 James R. Barlow: github.com/jbarlow83
-set -euo pipefail
-set -x
-
-pip install --upgrade pip
-mkdir -p packages
-wget -q 'https://www.dropbox.com/s/vaq0kbwi6e6au80/unpaper_6.1-1.deb?raw=1' -O packages/unpaper_6.1-1.deb
-sudo dpkg -i packages/unpaper_6.1-1.deb
-
-if [ ! -f /usr/local/bin/qpdf ]; then
-	export QPDF_RELEASE='https://github.com/qpdf/qpdf/releases/download/release-qpdf-8.0.2/qpdf-8.0.2.tar.gz'
-	mkdir qpdf
-    wget -q $QPDF_RELEASE -O - | tar xz -C qpdf --strip-components=1
-    cd qpdf/
-	export PATH="/usr/local/opt/ccache/libexec:$PATH"
-    ./configure --prefix=/usr
-    make -j 2
-    sudo make install
-    cd ..
-fi