Use patchelf v0.8

Seems like 0.10 breaks Qt libraries which expect a symbol called
qt_version_tag in a specific section in the symbols. Patchelf breaks
this by apparently moving the symbols to another section
(section 15 vs. 13).
We found out by looking into the readelf outputs of libQt5Core.so.5.
@azubieta spotted the different numbers, and looked up their meaning.

linuxdeployqt uses the patchelf binaries Debian jessie provides, which
is 0.8. Therefore we try to build that version from source instead,
hoping that this version won't break libraries.

If that doesn't work either, we'll try with the pre-built binaries.

.travis.yml

@@ -27,7 +27,7 @@ matrix:
             - libfuse2:i386
 
 install:
-  - git clone https://github.com/NixOS/patchelf.git
+  - git clone https://github.com/NixOS/patchelf.git -b 0.8
   - cd patchelf
   - ./bootstrap.sh
   - if [ "$ARCH" == "i386" ]; then export EXTRA_CONFIGURE_ARGS=("--build=i686-pc-linux-gnu" "CFLAGS=-m32" "CXXFLAGS=-m32" "LDFLAGS=-m32"); fi