Update needed versions of some libraries

Fix #542.

docs/install.rst

@@ -4,8 +4,8 @@ Installing
 WeasyPrint |version| depends on:
 
 * CPython_ ≥ 3.4
-* cairo_ [#]_
-* Pango_
+* cairo_ ≥ 1.15.0 [#]_
+* Pango_ ≥ 1.29.3
 * CFFI_ ≥ 0.6
 * html5lib_ ≥ 0.999999999
 * cairocffi_ ≥ 0.5
@@ -14,7 +14,7 @@ WeasyPrint |version| depends on:
 * CairoSVG_ ≥ 1.0.20
 * Pyphen_ ≥ 0.8
 * pdfrw_ ≥ 0.4
-* Optional: GDK-PixBuf_ [#]_
+* Optional: GDK-PixBuf_ ≥ 2.25.0 [#]_
 
 .. _CPython: http://www.python.org/
 .. _cairo: http://cairographics.org/
@@ -69,9 +69,11 @@ If everything goes well, you’re ready to :doc:`start using </tutorial>`
 WeasyPrint! Otherwise, please copy the full error message and
 `report the problem <http://weasyprint.org/community/>`_.
 
-.. [#] cairo ≥ 1.12 is best but older versions should work too.
-       The test suite passes on cairo 1.8 and 1.10 with some tests marked as
-       “expected failures” due to behavior changes or bugs in cairo.
+.. [#] cairo ≥ 1.15 is best but older versions may work too. The test suite
+       passes on cairo 1.12 and 1.14, and passes with some tests marked as
+       “expected failures” on 1.8 and 1.10 due to behavior changes or bugs in
+       cairo. With cairo 1.14, WeasyPrint sometimes creates PDF files that may
+       not be correctly interpreted by GhostScript or CUPS.
 
 .. [#] Without it, PNG and SVG are the only supported image formats.
        JPEG, GIF and others are not available.