tox: Set skipsdist = true

Since our tests don't actually run against the installed package, no
point in waiting for an sdist to be built.

tox.ini

@@ -6,6 +6,7 @@
 [tox]
 envlist = py34,py35-cov,misc,vulture,flake8,pylint,pyroma,check-manifest
 distshare = {toxworkdir}
+skipsdist = true
 
 [testenv]
 # https://bitbucket.org/hpk42/tox/issue/246/ - only needed for Windows though
@@ -61,7 +62,6 @@ deps = {[testenv:mkvenv]deps}
 # cx_Freeze doesn't support Python 3.5 yet
 basepython = python3.4
 passenv = {[testenv]passenv}
-skip_install = true
 deps =
     {[testenv]deps}
     -r{toxinidir}/misc/requirements/requirements-cxfreeze.txt
@@ -124,7 +124,6 @@ commands =
 
 [testenv:pyroma]
 basepython = python3
-skip_install = true
 passenv =
 deps = -r{toxinidir}/misc/requirements/requirements-pyroma.txt
 commands =
@@ -132,7 +131,6 @@ commands =
 
 [testenv:check-manifest]
 basepython = python3
-skip_install = true
 passenv =
 deps = -r{toxinidir}/misc/requirements/requirements-check-manifest.txt
 commands =
@@ -140,7 +138,6 @@ commands =
 
 [testenv:docs]
 basepython = python3
-skip_install = true
 whitelist_externals = git
 passenv = TRAVIS_PULL_REQUEST
 deps =
@@ -156,7 +153,6 @@ commands =
 # PYTHON is actually required when using this env, but the entire tox.ini would
 # fail if we didn't have a fallback defined.
 basepython = {env:PYTHON:}/python.exe
-skip_install = true
 deps =
     -r{toxinidir}/misc/requirements/requirements-pip.txt
     -r{toxinidir}/requirements.txt
@@ -168,7 +164,6 @@ commands =
 
 [testenv:pyinstaller]
 basepython = python3
-skip_install = true
 deps =
     -r{toxinidir}/misc/requirements/requirements-pip.txt
     -r{toxinidir}/requirements.txt
@@ -178,7 +173,6 @@ commands =
     {envbindir}/pyinstaller --noconfirm misc/qutebrowser.spec
 
 [testenv:eslint]
-skip_install = True
 deps = -r{toxinidir}/misc/requirements/requirements-pip.txt
 whitelist_externals = eslint
 commands = eslint --color qutebrowser/javascript