Change pypy travis-ci PyPy build to 5.7 release

We no longer need a nightly build now that 5.7 is released (and the
current nightly 5.8 is failing).

.travis.yml

@@ -32,10 +32,10 @@ matrix:
   - os: osx
     osx_image: xcode7.3
     env: PYTHON=3.6 CPP=14 CLANG
-  # Test a PyPy 2.7 nightly build
+  # Test a PyPy 2.7 build
   - os: linux
     dist: trusty
-    env: PYPY=1 PYTHON=2.7 CPP=11 GCC=4.8
+    env: PYPY=5.7 PYTHON=2.7 CPP=11 GCC=4.8
     addons:
       apt:
         packages: [g++-4.8, cmake]
@@ -107,9 +107,9 @@ before_install:
   fi
   if [ -n "$CPP" ]; then export CPP=-std=c++$CPP; fi
   if [ "${PYTHON:0:1}" = "3" ]; then export PY=3; fi
-  if [ -n "$PYPY" ]; then
-    curl http://buildbot.pypy.org/nightly/trunk/pypy-c-jit-latest-linux64.tar.bz2 | tar -xj
-    export PYPY_BINARY=$(echo `pwd`/pypy-c-jit*/bin/pypy)
+  if [ "$PYPY" = "5.7" ]; then
+    curl -fSL https://bitbucket.org/pypy/pypy/downloads/pypy2-v5.7.0-linux64.tar.bz2 | tar -xj
+    export PYPY_BINARY=$(echo `pwd`/pypy2-v5.7.0-linux64/bin/pypy)
     export CMAKE_EXTRA_ARGS="-DPYTHON_EXECUTABLE:FILEPATH=$PYPY_BINARY"
   fi
   if [ -n "$DEBUG" ]; then export CMAKE_EXTRA_ARGS="-DCMAKE_BUILD_TYPE=Debug"; fi