Merge pull request #1191 from consideRatio/pr/unpin-r-irkernel

Remove conda buildpacks pin of r-irkernel to 1.2

repo2docker/buildpacks/conda/__init__.py

@@ -362,7 +362,7 @@ class CondaBuildPack(BaseImage):
                 (
                     "${NB_USER}",
                     r"""
-                ${{MAMBA_EXE}} install -p {0} r-base{1} r-irkernel=1.2 r-devtools -y && \
+                ${{MAMBA_EXE}} install -p {0} r-base{1} r-irkernel r-devtools -y && \
                 ${{MAMBA_EXE}} clean --all -f -y && \
                 ${{MAMBA_EXE}} list -p {0}
                 """.format(
@@ -385,7 +385,7 @@ class CondaBuildPack(BaseImage):
                 ),
                 (
                     "${NB_USER}",
-                    # Install a pinned version of IRKernel and set it up for use!
+                    # Register the jupyter kernel
                     r"""
                  R --quiet -e "IRkernel::installspec(prefix='{0}')"
                  """.format(